dovecot - Apr 2016 - lmtp_rcpt_check_quota = yes silently blocks mail if quota check fails

I have a user which has a quota-check that fails with 'Internal error', 
if I enable lmtp_rcpt_check_quota, the mail is silently tempfailed.

Actually it looks like lmtp_rcpt_check_quota=yes suppresses normal 
Info/Error logging, even on Director.
The MTA just gets " 451 4.3.0 <xxxx at xxx.xxx> Temporary internal
error
(in reply to end of DATA command)" from the director, but nothing is 
logged with lmtp_rcpt_check_quota=yes, anywhere.

-- 
Tom