deliver mail to mailbox subfolder via lmtp

[Markus Schulz]

hello,

i have a postfix which delivers all mails to a local cyrus-imapd 
(v2.2.13) with lmtp:
mailbox_transport = lmtp:unix:public/lmtp
and i have set the recipient_delimiter = +

# from cyrus.conf/SERVICES
lmtpunix        cmd="lmtpd" listen="/var/spool/postfix/public/lmtp" 
prefork=1 maxchild=30

# from imapd.conf
lmtpsocket: /var/spool/postfix/public/lmtp


now i'm trying to deliver a mail to the recipient foobar+folder at domain
and the mail should be placed in the $INBOX/folder from user foobar.

But this works only if i allow the post acl "p" to "anyone" on 
"user/foobar/folder".

localhost> lam user/foobar/folder
foobar lrswipcda
cyrus lrswipcda
anyone p

if i remove the post acl for anyone (default each folder can only be 
accessed from $user and cyrus) the mail was placed in $INBOX instead of 
$INBOX/folder. I don't get any errors in mail.log.

Which user was used to check the acl before delivery into a subfolder 
from lmtpd? 
Why it can deliver to $INBOX but not $INBOX/folder, even though both 
have the same acls?

regards
msc