I don't think I'm having the same issues as you guys, but last night something weird did happen in my game.
I built a house on a 30x20 lot with the walls basically going to 3 of the 4 borders of the lot which means 3 out of 4 sides of the entire lot are fair game for townies to walk past. And also, I built the walls without furnishing part of the house, and it has the Private Dwelling lot trait.
Well, Lily Feng freaked me out because while I was playing I noticed her standing in part of the unfurnished house. There are no doors on that side of the house, so on top of the fact that she wouldn't be on the lot anyways because it's a private dwelling, and my Sim doesn't know her, I don't know how she could have gotten in to the building itself. I left her there and continued to play thinking that if she got in some kind of way, then she can get herself out some kind of way. Well, that didn't happen. Instead, for about a day, she stood in my Sim's house without him even knowing she was there because he doesn't even have access to that part of the house. And then on top of that, Judith Ward somehow also found herself in that area of the house. And Judith and Lily decided that they would become friends and just stood around talking for like a day. I was thinking they would just die of hunger or something, but nothing was indicating that their needs were dropping. So finally, I had to go into build mode and alter the house to let them out. They walked out of the door and down the steps with no problem, as if they had just walked up the stairs and through the door initially.
I mentioned the conditions of the house and lot because I was thinking that due to the proximity of the house's structure to the sidewalk where Sims walk by, maybe that had something to do with why both of them got stuck in the house. I'm not entirely sure though.
