This is a minor but annoying behaviour. I use Word 2007 and click the Open icon or Ctrl+o. A box opens in which I can navigate to the file I want. I drag the handles on this box to get a much larger size for easier use. Similarly, after creating a file, I clcik on the Save As icon or F12 to get a similar box. Again, I make this much larger. Exactlty the same use is made of the Excel 2007 Open and Save As boxes.
After running CCleaner 2.25.1025 the size of these boxes was reset back to the default size. I discovered by trial and error that removing the tick from the Windows Explorer - Other Explorer MRUs prevented this resizing from happening. But of course this will prevent other desirable cleaning from taking place.
Hopefully the setting for remembering the sizes the user sets for Open and save As boxes could be left alone in a future update.