Strange empty folders 1 1 1 1 1

I just updated to the latest dovecot from 1.2 and it has been working great for most of my clients. But one client,who is using Outlook, has found that hundreds of folders have been created, e.g.

admin@domain Deleted Items 1 admin@domain Deleted Items 1 1 admin@domain Deleted Items 1 1 1 .... admin@domain Deleted Items 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

This appears to be affecting all folders in his account, across multiple accounts for his domain. It isn't affecting any other user, even other users using outlook.

All the folders are empty.

Just wondering if anyone has any suggestions or ideas why this is happening.

Thanks Samuel