I'm working with some complicated plastic parts that have a large number of face drafts, which obviously interfere with mating parts cleanly. However, ALL mates remotely near drafted faces are broken and will not work.

For example, a rectangular block and a rectangular slot, 3 coincident mates on 3 surfaces to totally constrain the part. All 3 surfaces are perpendicular. The first 2 mates work, but the third refuses to work. I use the evaluate "measure" tool to check angles between the surfaces and it claims they are parallel, but still the mates refuse to function, giving "would over define assembly" errors.

I've been having this problem for a couple weeks through a large number of assemblies both ones done by hand and those I've inherited to work on, I've tried completely redoing them from scratch, very carefully monitoring of surface angles still doesn't seem to make a difference. Any idea why/how this happens and how to prevent it short of complete removal of all face drafts from parts?