[Dovecot] [Bug] Case sensitive usernames and variables

[Неворотин Вадим]

Today I've found a very irritating bug:

I use

mail_location = maildir:/var/mail/%u/

in my dovecot.conf. And if user type Username, username, USERname etc at
login dovecot create a different Maildir's for one real user. But LDA works
corretly and save all messages to lowercase username mailbox. No problem,
add L:

mail_location = maildir:/var/mail/%Lu/

Then all works good. But I has also such namespace configuration:

namespace shared {
separator = /
prefix = &BCAEMARBBEEESwQ7BDoEOA-/%%u/
location = maildir:/var/mail/%%u:INDEX=/var/mail/%u/shared/%%u
subscriptions = no
list = children
}

And here I can't replace %u with %Lu, because dovecot write to dovecot.log:

IMAP(malamut): Error: Namespace '&BCAEMARBBEEESwQ7BDoEOA-/%Lu/': shared:
Shared namespace prefix contains unknown variables

So user has only one mailbox (with lovercase name), but a lot of different
indexes for shared mailboxes, eg /var/mail/username/shared,
/var/mail/USERname/shared etc.

How can I tune dovecot to use always lowercase username?

Dovecot 1.2.10