Not a mask, a path. Clipping paths by themselves have no effect on pixels in Photoshop. They are for the benefit of external applications. Look in your Paths palette for a clipping path, not the Layers palette (the name of the path will be white with a black outline). Then delete it. Or just change it to a regular path.
If we were talking about masks, then you wouldn't see the shadow in Photoshop. Layer masks, clipping paths and clipping masks are three different things.