I haven't yet seen this in my game, and over on the forums, a player had uploaded their bugged build to the Gallery. When I downloaded it, all of the walls were in place in my game. I am using a fresh save that I created after applying the patch, clearing my cache, and repairing the game (steps I always follow for testing after each patch), so I am wondering if people are seeing this in older saves, by any chance. Also, are you building on a lot and then notice the problem, or noticing it right after placing the lot?
Edit to add that I have now witnessed the problem in a home I downloaded from the Gallery. It appears as if the room has somehow been corrupted. It seems that drawing a new room in place of the old fixes it, as after I did that, saved the lot to the library, and re-placed it, the walls remained. However, other methods I tried, such as just moving the room to another location, did not work.