I think I figured out your mate issue, and it should have given me a heads up. When you are choosing surfaces to be coincident on the threaded surfaces and the bolts or what ever you are mating up. When I did this with one of these peices, it didn't know what to mate to since I must have picked the threaded surface versus the non-threaded surface when I was doing the original mates.
I am guessing that this is what you ran into. Now I am just going to have to be doubly sure what I am clicking on for those mates.