Mailbox does not exist for mailboxes with '.'

[Сергей Осипов]

In imapd.conf I have option "unixhierarchysep: yes".
If I create mailbox with char '.', for example 'test.test', Cyrus pop3d write to log:
Feb 24 22:35:07 pop3[22096]: login: XXXX.XXXX.ru [XXX.XXX.XXX.XXX] test.test plaintext User logged in
Feb 24 22:35:12 pop3[22096]: Unable to locate maildrop for test.test: Mailbox does not exist

Cyrus IMAP write to log same string.

If I create mailbox 'test_test', all works.
Why Cyrus server can't find mailbox ?