Something wrong with rumour?
I have two races who know each other; Lithosoid and Dryad. I went to a Lithosoid world and tried to start a rumour about Dryad. The only race in the drop down was Lithosoid, which doesn't make sense... I ran the rumour anyway and no message was given at all on the success/failure of the rumour. I restarted the game and went to another Lithosoid planet. This time I could only select Dryad from the race drop down. Same on the world where the original bug occurred.
I have seen this type of issue sporadically since the original beta. Previously, I had even seen the race drop down empty, even though a number of races were known.