When you say “less sloppy”, how do you mean, Paul? Using groups and components is an essential part of working in SU, so how do you avoid the intersection issue?
I think I have just discovered why this drawing is causing problems when others haven’t. It’s to do with visibility of lines. I usually make my floor a Group and my walls another. In past drawings, I have just hidden the joining line in elevations, which is not a line I need to dimension. But in this case, I had hidden all the lines defining the base of the walls including the internal ones.
Actually, I think this may be a useful lesson for the unwary. It doesn’t seem to me to be necessarily intuitive that a line that is there but hidden should also be unavailable for dimensioning.
I guess I can delete those Groups from Slices now!