[Dovecot] Can't create subfolders when activating namespaces, e.g. private/public

Hi, i am using hardy dovecot, 1.0.10. If i enable namespaces (the private and a public one) i am unable to create new subfolders in my private namespace, only top level folders works. There is nothing in the log about that error even if i set mail_debug = yes.

If i comment out everything (no namespaces at all, implicit private one), it works again.

Any hints whats going wrong, why is my client getting the message about not being able to create this subfolder?

kinds regards

Torsten