diff --git a/LUA_API.rst b/LUA_API.rst
index bd2d33cb0..9ecd2e55e 100644
--- a/LUA_API.rst
+++ b/LUA_API.rst
@@ -693,7 +693,7 @@ Units module
 
 * ``dfhack.units.getPosition(unit)``
 
-  Returns true *x,y,z* of the unit; may be not equal to unit.pos if caged.
+  Returns true *x,y,z* of the unit, or *nil* if invalid; may be not equal to unit.pos if caged.
 
 * ``dfhack.units.getContainer(unit)``
 
@@ -752,7 +752,7 @@ Items module
 
 * ``dfhack.items.getPosition(item)``
 
-  Returns true *x,y,z* of the item; may be not equal to item.pos if in inventory.
+  Returns true *x,y,z* of the item, or *nil* if invalid; may be not equal to item.pos if in inventory.
 
 * ``dfhack.items.getGeneralRef(item, type)``
 
diff --git a/Lua API.html b/Lua API.html
index d44d82bab..7ce777c42 100644
--- a/Lua API.html	
+++ b/Lua API.html	
@@ -935,7 +935,7 @@ a lua list containing them.</p>
 <h3><a class="toc-backref" href="#id16">Units module</a></h3>
 <ul>
 <li><p class="first"><tt class="docutils literal">dfhack.units.getPosition(unit)</tt></p>
-<p>Returns true <em>x,y,z</em> of the unit; may be not equal to unit.pos if caged.</p>
+<p>Returns true <em>x,y,z</em> of the unit, or <em>nil</em> if invalid; may be not equal to unit.pos if caged.</p>
 </li>
 <li><p class="first"><tt class="docutils literal">dfhack.units.getContainer(unit)</tt></p>
 <p>Returns the container (cage) item or <em>nil</em>.</p>
@@ -982,7 +982,7 @@ or raws. The <tt class="docutils literal">ignore_noble</tt> boolean disables the
 <h3><a class="toc-backref" href="#id17">Items module</a></h3>
 <ul>
 <li><p class="first"><tt class="docutils literal">dfhack.items.getPosition(item)</tt></p>
-<p>Returns true <em>x,y,z</em> of the item; may be not equal to item.pos if in inventory.</p>
+<p>Returns true <em>x,y,z</em> of the item, or <em>nil</em> if invalid; may be not equal to item.pos if in inventory.</p>
 </li>
 <li><p class="first"><tt class="docutils literal">dfhack.items.getGeneralRef(item, type)</tt></p>
 <p>Searches for a general_ref with the given type.</p>
diff --git a/library/Core.cpp b/library/Core.cpp
index 7f08f402f..e8c43b7f5 100644
--- a/library/Core.cpp
+++ b/library/Core.cpp
@@ -71,6 +71,7 @@ using namespace DFHack;
 using namespace tthread;
 using namespace df::enums;
 using df::global::init;
+using df::global::world;
 
 // FIXME: A lot of code in one file, all doing different things... there's something fishy about it.
 
@@ -1017,7 +1018,7 @@ int Core::Update()
     Lua::Core::Reset(out, "DF code execution");
 
     if (first_update)
-        plug_mgr->OnStateChange(out, SC_CORE_INITIALIZED);
+        onStateChange(out, SC_CORE_INITIALIZED);
 
     // detect if the game was loaded or unloaded in the meantime
     void *new_wdata = NULL;
@@ -1043,11 +1044,11 @@ int Core::Update()
 
         // and if the world is going away, we report the map change first
         if(had_map)
-            plug_mgr->OnStateChange(out, SC_MAP_UNLOADED);
+            onStateChange(out, SC_MAP_UNLOADED);
         // and if the world is appearing, we report map change after that
-        plug_mgr->OnStateChange(out, new_wdata ? SC_WORLD_LOADED : SC_WORLD_UNLOADED);
+        onStateChange(out, new_wdata ? SC_WORLD_LOADED : SC_WORLD_UNLOADED);
         if(isMapLoaded())
-            plug_mgr->OnStateChange(out, SC_MAP_LOADED);
+            onStateChange(out, SC_MAP_LOADED);
     }
     // otherwise just check for map change...
     else if (new_mapdata != last_local_map_ptr)
@@ -1058,7 +1059,7 @@ int Core::Update()
         if (isMapLoaded() != had_map)
         {
             getWorld()->ClearPersistentCache();
-            plug_mgr->OnStateChange(out, new_mapdata ? SC_MAP_LOADED : SC_MAP_UNLOADED);
+            onStateChange(out, new_mapdata ? SC_MAP_LOADED : SC_MAP_UNLOADED);
         }
     }
 
@@ -1071,15 +1072,12 @@ int Core::Update()
         if (screen != top_viewscreen) 
         {
             top_viewscreen = screen;
-            plug_mgr->OnStateChange(out, SC_VIEWSCREEN_CHANGED);
+            onStateChange(out, SC_VIEWSCREEN_CHANGED);
         }
     }
 
-    // notify all the plugins that a game tick is finished
-    plug_mgr->OnUpdate(out);
-
-    // process timers in lua
-    Lua::Core::onUpdate(out);
+    // Execute per-frame handlers
+    onUpdate(out);
 
     // Release the fake suspend lock
     {
@@ -1116,6 +1114,34 @@ int Core::Update()
     return 0;
 };
 
+extern bool buildings_do_onupdate;
+void buildings_onStateChange(color_ostream &out, state_change_event event);
+void buildings_onUpdate(color_ostream &out);
+
+static int buildings_timer = 0;
+
+void Core::onUpdate(color_ostream &out)
+{
+    // convert building reagents
+    if (buildings_do_onupdate && (++buildings_timer & 1))
+        buildings_onUpdate(out);
+
+    // notify all the plugins that a game tick is finished
+    plug_mgr->OnUpdate(out);
+
+    // process timers in lua
+    Lua::Core::onUpdate(out);
+}
+
+void Core::onStateChange(color_ostream &out, state_change_event event)
+{
+    buildings_onStateChange(out, event);
+
+    plug_mgr->OnStateChange(out, event);
+
+    Lua::Core::onStateChange(out, event);
+}
+
 // FIXME: needs to terminate the IO threads and properly dismantle all the machinery involved.
 int Core::Shutdown ( void )
 {
diff --git a/library/PluginManager.cpp b/library/PluginManager.cpp
index 320e8dec8..ae8cc755f 100644
--- a/library/PluginManager.cpp
+++ b/library/PluginManager.cpp
@@ -609,8 +609,6 @@ void PluginManager::OnStateChange(color_ostream &out, state_change_event event)
     {
         all_plugins[i]->on_state_change(out, event);
     }
-
-    Lua::Core::onStateChange(out, event);
 }
 
 // FIXME: doesn't check name collisions!
diff --git a/library/include/Core.h b/library/include/Core.h
index fe83715cf..7da633cca 100644
--- a/library/include/Core.h
+++ b/library/include/Core.h
@@ -68,6 +68,17 @@ namespace DFHack
         class df_window;
     }
 
+    enum state_change_event
+    {
+        SC_WORLD_LOADED = 0,
+        SC_WORLD_UNLOADED = 1,
+        SC_MAP_LOADED = 2,
+        SC_MAP_UNLOADED = 3,
+        SC_VIEWSCREEN_CHANGED = 4,
+        SC_CORE_INITIALIZED = 5,
+        SC_BEGIN_UNLOAD = 6
+    };
+
     // Core is a singleton. Why? Because it is closely tied to SDL calls. It tracks the global state of DF.
     // There should never be more than one instance
     // Better than tracking some weird variables all over the place.
@@ -162,6 +173,9 @@ namespace DFHack
         int SDL_Event(SDL::Event* event);
         bool ncurses_wgetch(int in, int & out);
 
+        void onUpdate(color_ostream &out);
+        void onStateChange(color_ostream &out, state_change_event event);
+
         Core(Core const&);              // Don't Implement
         void operator=(Core const&);    // Don't implement
 
diff --git a/library/include/PluginManager.h b/library/include/PluginManager.h
index 7f98bf422..02974f36b 100644
--- a/library/include/PluginManager.h
+++ b/library/include/PluginManager.h
@@ -65,16 +65,6 @@ namespace DFHack
     // Close a plugin library
     void ClosePlugin (DFLibrary * plugin);
 
-    enum state_change_event
-    {
-        SC_WORLD_LOADED = 0,
-        SC_WORLD_UNLOADED = 1,
-        SC_MAP_LOADED = 2,
-        SC_MAP_UNLOADED = 3,
-        SC_VIEWSCREEN_CHANGED = 4,
-        SC_CORE_INITIALIZED = 5,
-        SC_BEGIN_UNLOAD = 6
-    };
     struct DFHACK_EXPORT CommandReg {
         const char *name;
         int (*command)(lua_State*);
diff --git a/library/lua/dfhack/buildings.lua b/library/lua/dfhack/buildings.lua
index ad82da89a..af9ad2605 100644
--- a/library/lua/dfhack/buildings.lua
+++ b/library/lua/dfhack/buildings.lua
@@ -178,7 +178,20 @@ local building_inputs = {
     },
     [df.building_type.Slab] = { { item_type=df.item_type.SLAB } },
     [df.building_type.NestBox] = { { has_tool_use=df.tool_uses.NEST_BOX, item_type=df.item_type.TOOL } },
-    [df.building_type.Hive] = { { has_tool_use=df.tool_uses.HIVE, item_type=df.item_type.TOOL } }
+    [df.building_type.Hive] = { { has_tool_use=df.tool_uses.HIVE, item_type=df.item_type.TOOL } },
+    [df.building_type.Rollers] = {
+        {
+            name='mechanism',
+            item_type=df.item_type.TRAPPARTS,
+            quantity=-1,
+            vector_id=df.job_item_vector_id.TRAPPARTS
+        },
+        {
+            name='chain',
+            item_type=df.item_type.CHAIN,
+            vector_id=df.job_item_vector_id.CHAIN
+        }
+    }
 }
 
 --[[ Furnace building input material table. ]]
@@ -318,7 +331,8 @@ local trap_inputs = {
             item_type=df.item_type.TRAPPARTS,
             vector_id=df.job_item_vector_id.TRAPPARTS
         }
-    }
+    },
+    [df.trap_type.TrackStop] = { { flags2={ building_material=true, non_economic=true } } }
 }
 
 --[[ Functions for lookup in tables. ]]
diff --git a/library/modules/Buildings.cpp b/library/modules/Buildings.cpp
index 65cf009f3..e0afc56ed 100644
--- a/library/modules/Buildings.cpp
+++ b/library/modules/Buildings.cpp
@@ -66,6 +66,7 @@ using namespace DFHack;
 #include "df/building_screw_pumpst.h"
 #include "df/building_water_wheelst.h"
 #include "df/building_wellst.h"
+#include "df/building_rollersst.h"
 
 using namespace df::enums;
 using df::global::ui;
@@ -86,6 +87,58 @@ static uint8_t *getExtentTile(df::building_extents &extent, df::coord2d tile)
     return &extent.extents[dx + dy*extent.width];
 }
 
+/*
+ * A monitor to work around this bug, in its application to buildings:
+ *
+ * http://www.bay12games.com/dwarves/mantisbt/view.php?id=1416
+ */
+bool buildings_do_onupdate = false;
+
+void buildings_onStateChange(color_ostream &out, state_change_event event)
+{
+    switch (event) {
+    case SC_MAP_LOADED:
+        buildings_do_onupdate = true;
+        break;
+    case SC_MAP_UNLOADED:
+        buildings_do_onupdate = false;
+        break;
+    default:
+        break;
+    }
+}
+
+void buildings_onUpdate(color_ostream &out)
+{
+    buildings_do_onupdate = false;
+
+    df::job_list_link *link = world->job_list.next;
+    for (; link; link = link->next) {
+        df::job *job = link->item;
+
+        if (job->job_type != job_type::ConstructBuilding)
+            continue;
+        if (job->job_items.empty())
+            continue;
+
+        buildings_do_onupdate = true;
+
+        for (size_t i = 0; i < job->items.size(); i++)
+        {
+            df::job_item_ref *iref = job->items[i];
+            if (iref->role != df::job_item_ref::Reagent)
+                continue;
+            df::job_item *item = vector_get(job->job_items, iref->job_item_idx);
+            if (!item)
+                continue;
+            // Convert Reagent to Hauled, while decrementing quantity
+            item->quantity = std::max(0, item->quantity-1);
+            iref->role = df::job_item_ref::Hauled;
+            iref->job_item_idx = -1;
+        }
+    }
+}
+
 uint32_t Buildings::getNumBuildings()
 {
     return world->buildings.all.size();
@@ -289,6 +342,10 @@ bool Buildings::getCorrectSize(df::coord2d &size, df::coord2d &center,
         makeOneDim(size, center, direction);
         return true;
 
+    case Rollers:
+        makeOneDim(size, center, (direction&1) == 0);
+        return true;
+
     case WaterWheel:
         size = df::coord2d(3,3);
         makeOneDim(size, center, direction);
@@ -592,6 +649,12 @@ bool Buildings::setSize(df::building *bld, df::coord2d size, int direction)
             obj->direction = (df::screw_pump_direction)direction;
             break;
         }
+    case Rollers:
+        {
+            auto obj = (df::building_rollersst*)bld;
+            obj->direction = (df::screw_pump_direction)direction;
+            break;
+        }
     case Bridge:
         {
             auto obj = (df::building_bridgest*)bld;
@@ -881,7 +944,11 @@ bool Buildings::constructWithFilters(df::building *bld, std::vector<df::job_item
         if (items[i]->quantity < 0)
             items[i]->quantity = computeMaterialAmount(bld);
 
-        job->job_items.push_back(items[i]);
+        /* The game picks up explicitly listed items in reverse
+         * order, but processes filters straight. This reverses
+         * the order of filters so as to produce the same final
+         * contained_items ordering as the normal ui way. */
+        vector_insert_at(job->job_items, 0, items[i]);
 
         if (items[i]->item_type == item_type::BOULDER)
             rough = true;
@@ -891,6 +958,8 @@ bool Buildings::constructWithFilters(df::building *bld, std::vector<df::job_item
             bld->mat_index = items[i]->mat_index;
     }
 
+    buildings_do_onupdate = true;
+
     createDesign(bld, rough);
     return true;
 }
@@ -954,3 +1023,4 @@ bool Buildings::deconstruct(df::building *bld)
 
     return true;
 }
+
diff --git a/library/modules/Items.cpp b/library/modules/Items.cpp
index f1d495bf1..335d7d8fc 100644
--- a/library/modules/Items.cpp
+++ b/library/modules/Items.cpp
@@ -69,6 +69,7 @@ using namespace std;
 #include "df/general_ref_unit_itemownerst.h"
 #include "df/general_ref_contains_itemst.h"
 #include "df/general_ref_contained_in_itemst.h"
+#include "df/vermin.h"
 
 using namespace DFHack;
 using namespace df::enums;
@@ -512,9 +513,12 @@ df::coord Items::getPosition(df::item *item)
 {
     CHECK_NULL_POINTER(item);
 
-    if (item->flags.bits.in_inventory ||
-        item->flags.bits.in_chest ||
-        item->flags.bits.in_building)
+    /* Function reverse-engineered from DF code. */
+
+    if (item->flags.bits.removed)
+        return df::coord();
+
+    if (item->flags.bits.in_inventory)
     {
         for (size_t i = 0; i < item->itemrefs.size(); i++)
         {
@@ -532,15 +536,31 @@ df::coord Items::getPosition(df::item *item)
                     return Units::getPosition(unit);
                 break;
 
-            case general_ref_type::BUILDING_HOLDER:
+            /*case general_ref_type::BUILDING_HOLDER:
                 if (auto bld = ref->getBuilding())
                     return df::coord(bld->centerx, bld->centery, bld->z);
+                break;*/
+
+            default:
                 break;
+            }
+        }
+
+        for (size_t i = 0; i < item->specific_refs.size(); i++)
+        {
+            df::specific_ref *ref = item->specific_refs[i];
+
+            switch (ref->type)
+            {
+            case specific_ref_type::VERMIN_ESCAPED_PET:
+                return ref->vermin->pos;
 
             default:
                 break;
             }
         }
+
+        return df::coord();
     }
 
     return item->pos;
@@ -625,6 +645,10 @@ bool DFHack::Items::moveToContainer(MapExtras::MapCache &mc, df::item *item, df:
     CHECK_NULL_POINTER(item);
     CHECK_NULL_POINTER(container);
 
+    auto cpos = getPosition(container);
+    if (!cpos.isValid())
+        return false;
+
     if (!detachItem(mc, item))
         return false;
 
@@ -635,7 +659,7 @@ bool DFHack::Items::moveToContainer(MapExtras::MapCache &mc, df::item *item, df:
     {
         delete ref1; delete ref2;
         Core::printerr("Could not allocate container refs.\n");
-        putOnGround(mc, item, getPosition(container));
+        putOnGround(mc, item, cpos);
         return false;
     }
 
diff --git a/library/xml b/library/xml
index b0d8e71dc..ab102b93f 160000
--- a/library/xml
+++ b/library/xml
@@ -1 +1 @@
-Subproject commit b0d8e71dc9f6e697409bd999801097acdc57fcd8
+Subproject commit ab102b93fca9b1ae8b5fbfc3ae5a9ee06ee60811