I am trying to create a snap hook feature, in the context of an assembly, so that the feature will align and position properly to it's mating part, parametrically.  The hook feature is to be on the inside face of a plastic housing half, to hold a circuit board within the assembled housing halves.  Attached is virtually exactly what I'm trying to create.

The inside face of the housing (that the base of the snap hook is to be attached) is a shelled feature that makes up the wall thickness of the housing half.  Also, it does have a curvature to it as well.  What is shown in this picture was a rough concept that I had done on an imported featureless model, which I had no issues with.

I am now recreating the housing model from scratch so that I can have a feature tree for adjustments.  However, when I get to this snap hook feature it will fail, for lack of a better term.  But not "really" fail exactly.  When I am going through the process of creating it, the preview shows up correctly.  However, when I click the check to finish the feature, it acts like it is building the feature correctly (it exits without error).  However, all that I'm left with in the feature tree is a 3D Sketch with a position point, no snap hook feature.

What's going on here?!?  Could it be that the snap feature won't build on the new recreated model, since the attachment face is part of a shell feature, on this new model?  I wouldn't think that would be the reason...  Has anyone seen this before?  Can anyone explain how to make this work?