I just found a bug that affects trading with other leaders using v68:
When you make an offer they don't accept, all interface elements vanish and all you see is the blank leaderscreen and the rotating earth-shaped cursor. All you can do from there is pressing Esc to go back to the worldview.
I started a new game to reproduce the error, and when making an offer they won't accept it just went back to the main-screen for trading, and the leader did not comment the offer at all.
When clicking on 'trade' again, the offer was still there. So either way it's not working as it should.
In situations where you are the one making the offer that's not a big deal, but when they offere something and you want to negotiate, it's pretty annoying.
I switched to v66 to verify it's an issue of v68, and everything worked fine there!
I'm not using any of the STFU-mods, so maybe it is connected to this new element?
edit:
I've noticed 1 more thing: When there is scenario #2 (the offer just closes and they don't comment it, when clicking on 'trade' the offer is still there), they will always start commenting it the third time you try it. Without exceptions. As long as you don't make any edits to the offer.
Just in case this helps figuring out what the problem is.