[Photoshop CS5] Memory usage doesn't change after clsoing work

[Tonic]

There's something I don't understand. When I'm done with heavy work, after closing it inside Photoshop, the memory usage doesn't change - the value is same as with opened work. Purging Undo/Clipboard/History content doesn't help, either. The only solution I know is closing and opening Photoshop again. But this is a barbaric method - isn't there more elegant one?

[ikken]

I mentioned it today too - I was doing some heavy content-aware filling for a picture background, and after 5 or 6 runs content filler just stopped working with a low ram warning;
neither purging the clipboard nor closing documents helped, restarting PS did the trick.