So I was on this quest following this person, I was walking for about 8 minutes. Everything was fine, until She went down this little hill and disappeared. I was looking around, no sign of her. Then I looked on the radar map at the top to see an arrow (showing where this woman was). I looked on the map, to find she appeared back to where the quest was started. I fast travelled back and she was saying things, what she would of said if she didn't disappear. For example; "This is a nice building" and we were crossing a bridge. She would off said this when she was next to the house, which is where we would off been if she didn't disappear.
This happened twice in a different location on the same quest. Then, it started happening more frequently at different intervals on different people. Don't know whether this is because of the 1.2 patch. But never happened to me before the patch.