cyradm --authz --user selecting wrong mailbox on Mac OS X

[Frederik]

I run this command on a Mac OS X 10.5 server running cyrus (version 2.3.8
IIRC):

/usr/bin/cyrus/admin/cyradm -user cyradm -authz user -auth plain localhost

This should select the mailbox for "user" and not the one from cyradm,
right?

Because this does not seem to work on this system: lm shows the mailboxes
for cyradm and the mail folders for user are visible in "Other Users/".

Of course I have a line
admins: cyradm
in imapd.conf.

What could be wrong? Does not this work in Cyrus as included in Mac OS X
10.5 server?

-- 
Frederik