I moved away (to an external drive) about 30 GB of files from a drive (startup disk) that had 60 GB of free space. After the move it still shows only 60 GB of free space, not 90, as I would expect. The trash is emptied.
I tried rebooting and verifying the disk (no problems found), but it didn't change anything.
How can I diagnose and fix the problem?
Note: this is what happened during the move. I deleted the "washed out" items and repeated the move.
Update: The space was being taken up by Time Machine's Mobile Backups feature. This has solved the problem.