This is running version 1.3 - I just had this happen. If you get the quest to tame ascian, but then trade the collar to a different hero, and then the _other_ hero uses the collar to tame ascian, what I'm seeing is that ascian gets tamed, and shows as one of your units, but cannot be moved - the orders have no effect. You _can_ tell ascian to 'explore', and off she goes, but otherwise you can't control her.

[EDIT] confirmed that it's the hero-switching that caused the bug - went to an earlier reload, kept the collar with the original hero, and ascian converted no problems.