Fess,

You have created the UV mapping on Low polys. Converting the geometry from from poly to SubD has chnaged to layout of the UV's therefore changing the mapping and the look of the model.

There is a way to keep the UV mappping assigned to thr Polygon Mesh, when you convert it but as I am at work, I cant 100% advise as I dont have Maya to hand .

Check out the Help file in Maya I am sure there is info on this in there.