Hey.

I Know that CS5 is a very new version, and they have many bugs before a first update. 
For check if fined problem / bug is a personal problem, or not. 

The bug what I fined, is with Smart Objects that was created automatic with Min Bridge, after drop the image at document. When I make changes at Smart Object,, they don't saved.
I use Photoshop CS5 ME (not extanded) version. 
Have you too this bug? 

The extanded version, don't have this bug.