[Dovecot] Access to the root of a shared mailbox

I have an issue with shares mailboxes

Example : I have 2 users A and B. A must have an access to all mail of B So i create a public namespace

namespace public { separator = / prefix = Public/ location = maildir:/home/users/B/Maildir }

It's OK for the subfolders, but not for the root (B's inbox, the most
important !)

it's seems to be like
http://www.dovecot.org/list/dovecot/2007-October/025965.html it's the only feature that prevents me to migrate from Courier-IMAP !