Steps to reproduce:

1. Create 2 LDAP connections, with 2 different domains.
2. Create a user and assign them a group with the ldap server as authentication that is not set as default
3. Try to login as that user, login not possible, zabbix is always using default ldap connection, and not the connection set from group.

Result:LDAP server is not selected from user group, 
See screenshot...
See log file...
See memory dump...
Expected:
See screenshot....
See attached patch file...