Possibly not a bug, but sure feels like one. After winning a war and getting a Truce state for 10 turns, the only diplomatic options I have is to start another war at a great Influence cost. So far so good. However, the losing empire can still roam in my influence zone in the meantime. I tried to go into their territory and couldn't because they had Closed Borders. Why can't I have Closed Borders as a winner? All they're doing is parking their ships in my systems and start another war in 10 turns from a much improved position.