Commander+Nevermore Interaction
I was just playing a game against a Geist of Saint Traft EDH deck and after naming the Geist, and then destroying it with a wipe, the AI managed to cast it on it's next turn. I know this is a bug because Geist should be able to be blocked by Nevermore since he's cast from the command zone and his hexproof doesn't kick in until he's actually cast. There's an archived bug report for the same problem, but it looks like it was either never fixed or was unfixed in one of the more recent updates. I'm running the newest version of Forge.