lmtp via unix socket and user+mbox@domain syntax

[Andreas]

I'm using postfix 2.0.19 and cyrus-imapd-2.2.4 (+patches from CVS)
and delivery is happening via lmtp unix socket. I'm trying to make
the user+mbox at domain syntax to work, but to no avail: all messages
end up in INBOX (I have set "recipient_delimiter = +" in postfix's main.cf).

Is it at all possible with this delivery method? Or only when using cyrus' 
deliver program?

Can I somehow bump up the debug level in lmtp to see what is going on?
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