I just experienced a massive bug with the Lich King hero power with Archlich Kel’Thuzad.
If you use the Lich King hero power to give an Eternal Knight reborn, then destroy that minion with Archlich Kel’Thuzad it permanently adds itself to your board after combat finishes. If you dont have room that Eternal knight if bounced back to your hand. You can even clone a golden version and it will stick on the board. It allowed me to summon 4 golden EK’s. This was in dous and I was able to solo the entire lobby.
Unless the reborn effect remains permanently I don’t really see where the bug is in what you’re describing
It’s not because the reborn is temporary that the spawned minion should disapear