Hello. r868.
Error result in screenshot 
Save file
hotkey_save.zip (4.5 MB)
release-868 (x64)[M]
stonehearth/services/client/widget/room_widget.lua:201: attempt to call method ‘is_fusing’ (a nil value)
stack traceback:
[C]: in function ‘is_fusing’
stonehearth/services/client/widget/room_widget.lua:201: in function ‘preview_data’
…nehearth/services/client/building/structure_tool.lua:403: in function ‘_on_dragging’
…nehearth/services/client/building/structure_tool.lua:151: in function ‘_on_mouse_input’
…nehearth/services/client/building/structure_tool.lua:94: in function ‘_mouse_cb’
stonehearth/services/client/input/input_capture.lua:55: in function ‘_dispatch’
stonehearth/services/client/input/input_service.lua:80: in function ‘_dispatch_input’
stonehearth/services/client/input/input_service.lua:12: in function <stonehearth/services/client/input/input_service.lua:11>