[Dovecot] Pigeonhole 0.2.2 - managesieve supports virtual namespaces?

[Tom Talpey]

I got around to trying the 0.2.2 managesieve listener and it's not
working for me. As soon as the client authenticates, the connection
is closed and the following is logged on the server:

> Dec 13 11:48:30 managesieve(xx at yy.com): Error: user xx at yy.com: Initialization failed: Namespace 'Mobile/': Unknown mail storage driver virtual
> Dec 13 11:48:30 managesieve(xx at yy.com): Error: Invalid user settings. Refer to server log for more information.

I do have such a virtual namespace defined in dovecot.conf, obviously,
and it works fine with dovecot 2.0.8. Additionally, the sieve plugin is
working fine for lda, dovecot's deliver is executing it perfectly.

Do I need to add a setting or plugin to "protocol managesieve" for this?
Combed the wiki to no avail.