Playing unstable version 1b. Large galaxy, 6 players - at least 2 opponents (of 4 I've encountered) are custom races. As stated, with 3 different AI opponents, the turn after I encountered them they believe we've been at peace a long time - often with +2 or +3 to the diplomatic bonus. Screenshot of the turn I encountered them (or a few turns later) and the diplomatic screen showing the errant bonus to diplomacy.
Sorry. Should have done that in the first place. Won't be home from work for 5.5 or 6 hrs. Will get you some saves once I'm home.
Ok, this is now fixed on the dev build. Races whom you have made recent contact will no longer report being at peace with you for a long time. This was happening in the case where those AI players had previous wars (not with you), which was mixing up their thoughts about peace towards other empires. As always, your supplied save was crucial to speed up the fix. Thanks!