This is how Bug works.
My [Mirage] created by [Spirit of the Badlands] became copy of [Astalor, the Protector] which was at the bottom of my deck sent there with [Sir Finley, Sea Guide]. My deck was left without minions to play so [Mirage] in my hand was always [Astalor, the Protector]. Couple of turns later I played [Astalor, the Protector] which gave me [Astalor, the Flamebringer]. HOWEVER game didn’t allowed me to play him. He wasn’t glowing as playable card in my hand even thou I was at 10 mana. The only so to say “World Effects” that were applied at that time were [Nozdormu the Timeless], [Kazakusan] and [Anachronos].
EDIT
After poking through 1 topic I’ve found the issue (well at least what is actual problem).
Cards that generate Temporary copies of [Astalor, the Bloodsworn] and [Astalor, the Protector] such as [Mirage] or [Fortune] (from priest legendary) causes bug on Manathirst (maybe?) which prevents next “stage” of Astalor to be played. You get an idea. Any card that generates Temporary version of first 2 stages of Astalor will prevent next one to be playable card and it will be stuck in your hand.