old received/sent messages are converted to drafts

One of our users, noticed that some of his mails in folders he created himself in zimbra web-interface have changed to draft format.
This has some annoying side-effects:

• these drafts can not be forwarded or replied to.
• when moved to the drafts folder, the sender changes to the owner of the drafts folder and the messages/drafts can not be moved back to the previous folder.

I read on several places: when folders behave strange, a re-indexation may help.
Re-indexation of the users mailbox did not seem to make any difference for this issue.

Anybody any experience with this?
Is there a way to (maybe CLI based) change messages from draft format into regular received emails?

Thanks,

Joost