OK, everything tested except for whether the notifications stop after 90 turns, because I haven't moved that far.
Also, I'm 99% sure I started this game in 1.0.0.20, and equally sure similar incidents didn't cause the bug in a 1.0.0.7 game.
peacedealbugtest has me at war with Russia, end turn once or twice and Russia will capitulate and offer both gold and gpt for 90 turns, in order to get 10 turns of enforced peace.
Go through 10 turns, and you will be told every turn that your peace deal with Russia has ended. German107 features this happening.
I kept playing, also had short wars with Japan and England. In both cases, they made peace by handing over straight gold and 90 turns of open borders.
German150 has repeated notifications of Japan's peace deal ending, and is about to start endless notifications of England's peace deal ending.
None of these are endless peace deals. I am able to declare on all 3, and in each case, it stops the notifications of that civ's peace deal. So my assumption is the bug is caused by one part of the deal being for 10 turns, one part for 90. And as I said, this did not happen in my first ever game, started under 1.0.0.7, though I did make 10 turn peace deals with 90 turn gpt parts.
Also, if you DoW Japan on turn 150, a research agreement that is less than 10 turns old will mature, giving Bronze Working to the player, and generating a 'Japan has entered the classical era' popup.