Why does my Mecanim mesh have dead vertices?

I have a model that I've exported from Blender. In Blender, it's rigged pretty well and vertices deform as expected, but when I import the model into Unity and attempt to test the various muscle groups, I have 2 clumps of dead vertices which are not deformed by any muscle movement. They are around the nipple area of the chest...it looks pretty funny actually, because my character now appears to have a healthy pair of man-boobs, but that's not really the effect I'm looking for. :)

Is there a way for me to experiment with the various bones in my rig and try to give them more "reach" or weight against those vertices? I have been playing with this all day, but have not been able to reach a satisfactory state.

This mesh is a template mesh that I intend to expend on and make my other characters from it, so it's important that I get this right otherwise all of my characters will have man-boobs.

I've attached an image with the model in various levels of "open" and "close" poses from the Mecanim muscle group editor. The dead vertex clumps are outlined in red.

Any thoughts?

Thanks,