I've decided to take the long route and conquer everyone.
Occasionally, some of the races that are nearly destroyed will over a Conditional or Unconditional surrender. When I accept I don't gain control of their ships and planets, just Enforced Peace. After a few turns, they declare war again. I've always been under the impression that Surrender meant that they give up and I get all their stuff. At the very least, I expected a Conditional Surrender to mean that they got to keep all their stuff, but they are my submissive ally.
But nope, they just declare war again and then offer a surrender a few turns after that.
Can someone explain if this is a bug, intended, or what?