Nature’s Blessings upon you! This is in regards to the card, “ARCHLICH KEL’THUZAD” with affect, “At the end of your turn, destroy the undead to the left of this and resummon an exact copy” is glitched and has been for a while. At this time the card in fact, removes the “REBORN” aspect instead of summoning an “EXACT” copy. Finally fed up with it! 
RESPECTFULLY,
KILLNAR BREEZELEAF,
NIGHT ELF DRUID
Saw it too happen too. I think it happens when your unit has reborn, it will be destroyed then reborn and if there is no place for copy it will get lost.
This is the intended interaction, not a bug. The destruction happens first, then the resummon. It’s up to you to manage your board space.
Okay that makes sense!