bug in group permission check

Jul 19 01:05:27 sv1 dovecot: auth: Error: passwd-file(aa@ddd,89...24,<>): stat(/usr/dovecot-cfg/dom-home/ddd/etc/ddd/shadow) failed: Permission denied (euid=33454(dovecot) egid=33454(dovecot) missing +x perm: /usr/dovecot-cfg/dom-home/ddd, we're not in group 33795(sysgroup), dir owned by 32072:33795 mode=0710)

root@sv1 [~]# sudo -u dovecot groups dovecot sysgroup

root@sv1 [~]# sudo -u dovecot cat /usr/dovecot-cfg/dom-home/ddd/etc/ddd/shadow <prints content of the file>

It seems that dovecot incorecly checks for group permissions not even trying to access file - probably cant handle that dovecot is part of more than 1 group. When its part of single group problem is not occuring.