This one got me searching errors from my boat model for hours and all this time it was just maya acting up on me

Try this:
- Create default polygon cube
- Assign few different shaders to couple of faces so that it has multiple materials
- Convert it to subd
- Do Subdiv Surfaces -> Clean Topology
-> BOOM... the surface is gone. Only wireframe left...

Does this happen to you?

Btw, I'm using maya 4.5...