So I started a tiny map with all the majors and 2 minors. The result was interesting, and fun. And through some clever UP manipulation and carefully planned planetary invasion, I won (though I've continued because I'm not done experimenting).
Throughout the game, I noticed several strange diplomacy screen bugs and inconsistencies in what the AI really think of me.
As the title implies, much of the AI's diplomatic posture is not reflected in their behavior, and many of the places their relationship to my civ is defined, the definitions don't match.
1) At War, Angry, and seemingly Neutral--all at once!

2) The Drengin seem to hate me... but they are "Neutral"

3) The Thalans are Happy with me... or not?

4) Races that hate me are the only ones that vote for me...

5) Diplomacy Screen icons misaligned with civs' planets. (And some icons displayed for defeated civs.)

All that being said, I love the new diplomacy screen--very intuitive and visually appealing.
Also, the bugs in the diplomacy didn't make the gameplay any less fun, overall. So I can only imagine how awesome gameplay will be with these bugs hammered out!
Great work on this Beta release!