rRPKae2bd007 has broken the LDAP search for delegation users. Related tickets in Bugzilla are
https://issues.kolab.org/show_bug.cgi?id=5019
https://issues.kolab.org/show_bug.cgi?id=5024
Resolved in git master rRPK2fcb1eba, rRPK97ea819 and also backported to Roundcube release-1.1 branch (rR15bcfbd5, rRb765160f) and to roundcubemail-plugins-kolab-3.2 in rRPK8cc7909c and rRPKf733eef1.
Please consider these changes for upcoming releases.