I wanted to share an issue that I came across, as well as the solution. I run a lot of welded components through COSMOS, so I insert a new part into an assembly, and then create a join feature in that part for the welded component I am going to test. One thing I have noticed is that if "Force Surface Contact" is checked, the new joined part won't always update if you change an individual component. Uncheck that box and it should update correctly.

SWX 2006 SP5.1 / COSMOS 2006 SP5.0