Yorick Ult Problem?

I was playing a normal 5v5 on Summoner's Rift with a Yorick on the enemy team. We were destroying their nexus with Maiden of the Mist out too. When we destroyed the nexus, the Maiden kept attacking during the Victory screen killing a person on my team. I found that really funny, but it still counted as a kill for Yorick and a death for my team member. I don't think it should happen, but it did. Has this or something like it happened too anyone else?