Yes, I do have the Auto Clean Up box checked, and I am only working on one layer. And, I'm only working in 2D, yet it chooses to occasionally, randomly, give some objets a third dimension. Once I see that two adjoining walls aren't cleaning up, I check them, see that one or two of them have some random Z coordinate, so I reset them to Z 0". Sometimes this works, sometimes it doesn't. When it doesn't work, I will delete the wall, or walls, in question and redraw them. And they still won't clean up. It seems once they don't clean up, they never will.
Thanks for the response, Bob.