You might have targeted the elite AI in the PZ or at the very border of the PZ, but when the real battle started the AI + fleet & yourself were outside the PZ,. That is why there was no boundary circle... Imo, that is not a bug... that is the risk of targeting an AI + fleet at the very edge of the PZ.
I made that mistake aslo, and i'm pretty sure it might have happened to some other players...