I solved the problem. I was reworking an old game made with A5 and some of the furniture in the room was prefabs. I replaced all of those prefabs with models with polygon set on. Now all's well. Since there was no problem with A5 I can only presume that levels made in A5 WED and A6 WED aren't compatible for collision purposes. Sounds like a dumb guess, LOL.

Now...if someone could give me a workaround to keep the mouse trapped in a window I would be done with this beast.