Exported emails not deleted from archive

Hi all.

I thought I had an issue with orphaned shortcut deletion but it turns out not to be the case.

To help a user delete several thousand emails from his archive I told him to copy them to a specific folder which I then "exported" with the option ticked to remove the exported items.

The export (.pst) has worked fine but the emails have not been removed from the archive.

What could be causing this?

thanks

Tracy