Could you please give a little more detail?  I can't think of any changes that we made that would affect the peace treaties. 

This isnt new.
This is a reported bug in diplomacy.
What happens is that sometimes when at war, during the computors turn, it would truce even if you did nothing to stimulate this.
Same thing can happen with war. Where one turn your at peace next turn the diplomacy screen or foreign policy screen shows you at war.

Yeah, now that you mention it, in my last game, I was the Iconians at war with the Drengin (or however it's spelled) and just as I was moving in to launch an attack, I noticed we were at peace again even though I had not initiated peace.

I assumed it was just me being absent-minded, but I guess it was this bug as well.

EDIT:
I can't produce a save game, but here were a few conditions that might help:

-I was allied with people who were also at war with the Drengies, and they had made peace
-I joined the war using the pop-up window that you get when someone declares war on an ally

Hmm, I have save games where this occured, but since it seems random I can't reliably produce it.

Let's see:

I was at war with the dregin.
I was allied with everyone except the Korx, Dregin, and Yor.
During the computers turn I agree to a peace treaty (w/o actually doing anything on my end)
I am notified of this treaty at the begining of my turn via a diplomacy icon.
I was Xeno-Ethics good.

What specific information would help you? I'm more then happy to provide whatever you need.

Perhaps when the AI made peace one of the terms was that the other AI made peace with you?

But the AI shouldn't be able to FORCE me to end my war.

Well, no. Obviously it would still be a bug. Are you technically weaker militarily? They might have thought they were doing you a favour...

Yea I was lower score wise militarily. Althogh my ships would have mopped the floor with them, being that I had good defense against their type of weapon.

I've played two games while not being good aligned, I haven't had it happen. I don't know if that's any more help.
I'm going to try playing as pure evil the next game, and then another as good.

Hope any info I'm giving helps.

This has happened to me a couple times too, and I'm guessing that it is because my ALLY signed a peace treaty with them (or they initiated one with my ally?) and somehow it cascaded down to all the other allies, me included.

"Oh, don't you remember signing that peace treaty? Were you drunk? What was her name?"
"It's all in the fine print about our alliance, subparagraph 412, section 1123..."

Still, they ask me to go to war with them (or terminate the alliance), it seems fitting that they should ask me to go to peace with them (or terminate the alliance).

Ok, it just happened agai. I'm good aligned, and one of my allies signed a peace treaty with the Yor and I automatically did it.

Same game, and I made a post about the topic. The Yor are wiped out, they surrendered to the Terran alliance 2 turns ago. Now I just got a notification that they changed Alignment.