Make Sure you have deleted all history. Sometimes a build up of history can play havoc with Maya commands.

Check: after combining make sure that you have merged vertices btween the ear and the head. this is most probably the case. Then have a look in the menu for convert to subd. If the face/mesh count value is lower than the actual models face count value just increase it

Also check: that there isnt any subd blind data nodes in the hypergraph. If there are just select and delete them. Failing any of this run the cleanup command (usually from edit polys menu) this will tell you whats wrong too.

Cheers
Jay