I was doing some tests with my current campaign (just clicking End turn to see what happens)... I played Brutii, in the middle of the Civil war. Julii ofered ceasefire, and I accepted it (under heavy conditions - I gave them a lot of money and 3 provinces). A few turns after Julii attacked, which wasn't surprising.

What surprised me was the fact that Julii were still shown as NEUTRAL! And when I attacked them, I got warning message that I'm about to attack neutral faction. I checked diplomacy screen, and there was no war between me and Julii.

So, basicaly, we were not in the war, but they still kept attacking me.

P.S. I have an image but don't know how to include it.