I have no experience with it from cast form, but I assume this bug relates more to the potion form, or possibly a lack of some documentation in the spell changes.
DISPLACEMENT- Duration increased to 3 rounds / level. In addition to normal effects (50% concealment on the target), the spell creates a MIRROR IMAGE out of the target.
There is no indication in the documentation that this applies only when the spell is CAST and the potion form seemed to last the normal 1 round/level(I could be wrong).