[Dovecot] Unable to delete folder in public namespace

[Max Ivanov]

I use public namespace for group mailboxes. Users are able to create
subfolders , but its impossible to delete them. thunderbird 2.0.0.21
complains: "Cant' rename mailbox to another storage type", both
namespaces (private and public) use same storage type, so I believe
that it's a namespace problem.

Is there any way to move folders between namespaces? Or maybe sieve
script or plugin which intercept move command and do the move to some
unsibscribible folder in public namespace.