Deleting files doesn't free up space [duplicate]

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.

The washed out appearance happened to me once on a failed copy, in my case the files all had an improper creation date. In fact changing the date on the file fixed the issue for me. I think I used the info on this page to change the created date of the files. http://blog.grapii.com/2010/07/change-a-files-creationmodified-date-on-mac-os-x/