Currently CCleaner displays same MS Office recent files (C:\Users\USER\Application Data\Microsoft\Office\Recent) multiple times as different Office versions:
upgrading office usually leaves the old office's registry keys. If you run regedit, you will find the office keys in currentuser\software\Microsoft. I'd give the full keys but am away from my pc at the moment.
There is another issue with ccleaner and MS 2010 / Windows 7. Running ccleaner resizes all of the dialogue boxes to their defaluts. And I cannot find the hooks to keep these unchanged.
The diaologe box size is not in index.dat (C:\Users\USER\Application Data\Microsoft\Office\Recent\index.dat). And I cannot find them in the registry. But whereever they are, ccleaner is cleaning them. And not reporting it.