Basically that - it could potentially cause a mess with trigger areas. But I'm not averse to adding it altogether; the details of how it works with the trigger area would just need to be worked out (keeping in mind that, the trigger areas are checked for at a lemming's foot, and objects are given their trigger areas with this in mind. Even simply for invert, the trigger area needs to be offset a bit from where it would be with a direct inversion).