Then maybe you didn't move, but copy? It's a checkbox easily overlooked.
If new documents go into the copy, and opening and updating an existing document updates the one in the copy, you can delete the original. To the recycle bin, to play safe!
After installing Windows 8 I moved "libraries/My documents" folder to another drive (I have SSD OS drive)
but still c: space keeps going low.
I found a folder on my c: drive named by my PC name on the network, e.g. "MyPC" that has 10 GB size and includes the following file tree: MyPC/Documents and settings/Administrator/desktop,Favorites,My documents.
"My documents" seems identical to the Users/Myname/My documents that has been moved to a different drive.
I am the only user and have administrators permissions. It seems this Administrator's folder duplicates my documents somehow. (it's desktop folder is different from MYname Desktop folder). What should I do to clean the space - try to login as administrator and do something about this huge duplicate folder?