Full merging of tickets - turn two tickets into one ticket

I've only used merging once or twice, and for requests from an external source, there's not much point the way it currently works.

For merging to be useful, two merged tickets should behave as one ticket. If ticket B has been closed and merged with A, then replies to B should be added to A, and not cause B to be reopened. If a ticket has been closed and merged in to another ticket, then the customer should not be able to reopen it.

An example
We had an open ticket (ticket A), related to a problem with one of our suppliers, affecting one of our customer.
We received a new email, from the customer, relating to the same problem reoccurring. As expected, this generated a new ticket (ticket B).
The requester at the customer end copied some colleagues on the request.
One of the colleagues hit reply all, to say thank you to the requester. I had expected this email to be added to the conversation for ticket B, but instead, a third ticket was created (ticket C)

I merged tickets B and C into A, since they all related to the same issue. I checked the box so that an email would not be sent to our customer to say that the merged ticket had been closed.

Just now, the customer replied again to ticket B, which, since the tickets have been merged, SHOULD have resulted in his reply being added to ticket A, but instead it re-opened ticket B. So, as far as I see, the merging is completely pointless, and serves no other purpose than being shorthand for manually adding a note saying "Closed, please see ticket A".


I'm sure some people will think that "if the requesters handle it right, and don't reply to a closed ticket, then the current functionality is fine". However, in the real world, customers are human, and they just want to send an email to support@ when they have a problem. They don't know, or care that you've got a ticketing system. They don't want to have to think about which email they reply to, and educating every one of your customers in how to use a ticketing system is just not reasonable.