Rare occurence, but when the elkowl gets rebirth, and returns from an egg he has lost all abilities and appears as a blank unit (no rebirth/X ability). This is unlike all other rebirth units, and the code reason is probably due to the opening gambit of the elkowl. Still, the blank unit does not make sense and it is an odd behaviour.
It makes perfect sense, and it works exactly like all other rebirth minions. Rebirth gives you the BASE card with whatever abilities the card has. The effects given by the opening gambit are not part of the card text; they act like buffs. For example, when a Young Silithar hatches, it won’t have any of the buffs it had when it was alive.
I agree that it’s non-intuitive, but it’s also consistent with how Rebirth works for other cards.
Rebirth minions in general will loose any buffs placed on them (such as Diretide Frenzy) when they go into egg form, since they hatch into a completely fresh version of the minion that died.
The bonuses that Elkowl gains from its Opening Gambit effect (including Rebirth itself) behave identically - the only difference is that none of the other Rebirth minions have effects printed on the card that would be lost through Rebirth.
It’s a strange design choice that Elkowl can get Rebirth from its effect in the first place, but that’s in the same sense that Ranged battle pets are a strange design choice - the functionality isn’t bugged.
It is completely intentional, not a bug. As the thread has been answered I am going to lock the thread.