Engine error when placing roof with stand alone structures

release-559 (x64)
stonehearth/lib/build_util.lua:739: assertion failed!
stack traceback:
[C]: ?
[C]: in function 'assert’
stonehearth/lib/build_util.lua:739: in function 'create_edge_loop_for_wall’
stonehearth/lib/build_util.lua:747: in function 'create_edge_loop_for_wall’
stonehearth/lib/build_util.lua:747: in function 'create_edge_loop_for_wall’
stonehearth/lib/build_util.lua:747: in function 'create_edge_loop_for_wall’
stonehearth/lib/build_util.lua:826: in function ‘calculate_roof_shape_around_walls’
…th/services/client/build_editor/grow_roof_editor.lua:116: in function ‘_compute_roof_region’
…th/services/client/build_editor/grow_roof_editor.lua:78: in function ‘fn’
…ces/client/selection/entity_or_location_selector.lua:233: in function ‘_get_selected_entity’
…ces/client/selection/entity_or_location_selector.lua:269: in function ‘_on_mouse_event’
…nehearth/services/client/selection/selector_base.lua:115: in function '_mouse_cb’
stonehearth/services/client/input/input_capture.lua:49: in function '_dispatch’
stonehearth/services/client/input/input_service.lua:55: in function '_dispatch_input’
stonehearth/services/client/input/input_service.lua:12: in function <stonehearth/services/client/input/input_service.lua:11>