I have also experienced this problem, for me it was happening consistently with one particular wall in one of my projects. I tried a variety of ways of trying to get it to draw itself correctly, all unsucessful. Eventually I just wrote down all the important parameters of the wall (hgt. fill....) erased the problem wall, and put a new one in its place and the problem went away. I don't know what caused the issue for me, SEO's, trim to roof.... or what... but when I have experienced this, it has been limited to a select few locations.
If you are just having this problem with a couple of walls then this approach might work for you, if this is happening with all your walls, then I don't know what to tell you.