[otrs] Notifications only sent to 3 users of a group instead of ALL

Hi all, we are using version 1.1.3 on a windows server with mySQL as DB. We have groups with more than 5 users attached to one ore more queues. When now e.g. the ticket is moved to a new queue, all members of the group which is linked to the just selected queue should get an email notification. For some reason only 3, and always the same 3, user will receive the mail notification. The other group members will not. Is there somewhere a setting or a line of code that needs to be changed in order to have ALL group- members notified ? Regards Ralf