Hi,
Are you selecting the sent items folder? In that screen shot it doesnt look like it. Though i wasnt able to identify the language. I thought it was German but Sent Items doesnt translate to what you have selected.
Other than selecting the wrong folder; can you check the account that performs the restores and see if it's in there? It may also be an exchange rule that deletes the sent items... Or the user may be downloading all their emails to a PST (not leaving a copy in the mailbox) and the restored emails are dissapearing to their pst before you can see them.
Matt