[GAMEPLAY] Destroying enemy nexus results in defeat

In my coop vs AI game ending about 530pCT today, we destroyed the enemy nexus, but the defeat animation came up. After clicking througha nd coming to the stats screen in the client, it was recorded as a defeat. Looking at the chat between the players, I suspect that it was not a defeat for anyone else - I didn't chat with anyone (I had to step away).

The only thing that seemed unusual about the game was that I was playing as Anivia and was dead (in egg form) at the time of the nexus kill.