I think you are using an older version of the Helpdesk/Ticketing system extension, just upgrade the extension from extension store on your instance and then I think this should work fine.
I think there is nothing with help desk module I have just rename the username, is there any relation between helpdesk module and user details modification?
Yes....there was a bug in the earlier version of the helpdesk module, because of which the notification was triggerred, we had fixed this sometime back.