Two things that I've noticed for a long time and never thought to report them

1) If you demand tribute and they say no, then click the "send" button again, the game acts as if they paid the extortion but nothing actually happened. Your relations with that civ suffers for it. If you come back later, that civ acts as if they've already paid you tribute previously.

2) If you have an interstellar government and trade "attack %civ%" to someone else, you can declare war on somebody without the senate voting first. Not really a problem, since the senate goes my way anyway, but I can't imagine it's supposed to do that.