I don't know of any relevant changes, but in my very old version, sometimes the AI will accept peace after you take a city (even when they wouldn't capitulate) and sometimes they will go from willing to accept peace to refusing it. I have seen both of these in the past 50 turns or so of my current game.
I believe the AI only offers peace at the start of their turn, i.e. before moving/attacking. However, in Let's Plays (and I've picked up the habit myself) the human player, wanting to make peace, will check for peace then attack and pillage leaving units in dangerous positions knowing peace is assured (obviously not taking a city). Feels like a bit of an exploit. Perhaps the AI's should reassess peace at the point when you ask in such a way that such play would be dangerous.