Undo creates duplicate faces
 

When i've converted an object to subD...sometimes i wanna undo everything i did, a few steps before the conversion...however, sometimes, when i undo, i get duplicate faces. it's still the same object, as i can select any face and it all turns green. is there a way to fix this? i don't want to have to copy, convert, delete converted just to avoid it. i've tried deleting history before converting, after receiving duplicates...deleting empty nodes in the hypergraph, etc...but nothing seems to work...it's really bothering me. i've had this problem on my friend's maya, and on my PLEs