After Amiri had played her Medusa Mask which "freezed" the monster and was supposed to return it on top of its deck at the end of the turn, she moved to a different location at the end of her turn as per character's ability. The monster moved with her and was "released" on top of her new location.

Ouch! There's a reason you put it back on top, right? So having it follow you truly sucks! Did it follow you back to the original Location?

Just made an account to state that the bug is still occurring. Recently got the game and experienced the same thing - used Medusa Mask with Amiri on a Villain (Mogmurian, specifically), then Amiri moved to another location at end of turn (and used Move-Other as well, in case that's relevant for replicating the bug), and then from the NEW location that Amiri moved to, the Villian was on top of the deck, whilst it had disappeared from the original location.

 

Very unsettling, since I'd moved her in preparation of temporarily closing that location to finish the scenario, and explored once more for a last-chance at loot; not to find the villain having teleported!