I have noticed a bug in my first game not sure if it has been reported before or not.
Back ground i have peace treaties with several AI's and a couple of Allies as well. 9 AI on normal.
A hostile AI luanches an attack on one of my planets and a Ally sends in a fleet to help defend the planet as i had no ships there. The Friendly ally ran but came back once it was clear i would keep the planet.
The whole time we have been allies and for some reason he has a huge fleet there in my gavity well now and I keep getting those threats from him that you get before just before they attack you (we are still allies).