vTiger 7.1 - HelpDesk Email does not merge values when sent to a Contact

When sending an Email from within a Helpdesk ticket, using an Email Template that contains merge fields e.g. helpdesk-ticket_no

If the email is sent to the Contact related to the Ticket (the default) then the merge fields are set correctly. If the email is ALSO sent to a different Contact (usign the search functionality), the merge fields are NOT populated, AND the email is also duplicated to the Contact related to the Ticket - who now recieves 2x Emails, 1 with merge fields correct, and 1 incorrect.

It appears to stem from line 106 & 107 in /modules/Emails/models/Record.php which calls getMergedDescription() and passes $parentModule. When $parentModule is 'HelpDesk' it works correctly. When parentModule is 'Contacts' it does not work. Should this not be determined by the module that the Email is sent FROM rather than what it is being sent TO? (parentModule is determined for each Recipient of the Email)