I’m doing a fairly straight forward cloth rig with body mesh connected to an nRigid node, and a pair of nCloth pants.  The body mesh is deformed via a blendshape from t-pose to start pose over 70 frames.  At the start frame everything looks fine.  Once the sim starts running the pants start to deform the nRigid collision shape (not that actual mesh).  If you don’t enable “Collision thickness” in the solver display of the nRigid, you would have no idea what was going on.
However if you look at the attached image 12 frame into the sim, you’ll see the green selected nRigid is not so rigid, but deforming.  I should mention that the nRigid has a collision strength of 0.8, but that shouldn’t make it deform...nothing should make it deform unless you're deforming the underlying mesh into that shape (which is not the case in this scenario).
I should add that there are three other garments in this setup (a jacket, a shirt and a tie), which were turned off for this sim.  They behave as expected and have no effect on the nRigid shape.

Any ideas, thoughts suggestions, similar problem?

looks like the culprit was collision layers for those that are intererested.  I was using non-integer numbers for my collision layers and that seems to cause bizzare shapes from the collision object.  Turning all the collision layers to 0 fixed the problem.