Line 502 of stonehearth/ui/game/unit_frame/unit_frame.js reads:
}.observes('model.stonehearth:siege_weapon', 'mode.stonehearth:iconic_form.root_entity.components.stonehearth:siege_weapon'),
I imagine mode should be model:
}.observes('model.stonehearth:siege_weapon', 'model.stonehearth:iconic_form.root_entity.components.stonehearth:siege_weapon'),