This is probably a known bug, but I thought I'd just bring to your attention that the AI, when taunting the player, (e.g. Haha! I am now researching XENO BIOLOGY! You're real screwed now!) fails to take into account whether it actually knows the player. Then of course we can conduct trade with some race who we've never even seen.
I like the taunts, but it seems probable that a few simple lines of code could add a check to see if the race has met the player before taunting. (Note: this might cause problems with the Dread Lords, who sometimes taunt the player, but without extra code might not be able to because they don't 'meet' us like the other races do.)
I carefully say 'might' and 'probable'. I don't want to insinuate that something's easy or a bug when it might not be. I'm just making assumptions.