I was assaulting a system that had 4 Drengin controlled planets. I conquered one and left 2 Paladins in orbit. Before my succeeding transports could arrive, the just conquered planet flipped back to Drengin control. I guess this was due to higher influence. However, the 2 ships I had left behind in orbit, were still there, but I could not move them. Subsequently, when another transport arrived I was unable to attack the planet, I couldn't even put the transport in orbit. The game behaved as if I still controlled the planet.
Has anyone else encountered this?