In my recent game, I got the Jagged Knife event. After a long war I tried to negotiate peace with them. I still wanted some low class planets in systems I controlled, so I clicked to add the planet I wanted and then clicked Peace Treaty. As soon as I clicked peace treaty, it crashed. Then I went back in and tried selecting peace treaty first, then the planet. Peace treaty went ok, but when I clicked the planet it crashed.

I have only tried this with the Jagged Knife and don't know if it would happen with any other minor race.