We get the Thank You as well, but we have accepted those emails. We simply reclose the ticket. I know it’s not what many others want, but that is a more difficult item to filter out.
But that could also solve your Problem.
I think it should be three options:
Reopen Ticket on answer. Very bad to us, as we bill closed tickets and reopening can cause billing the accounted time again.
Open New Ticket. You will have a lot of Spam “thank you” and auto answer Tickets.
Do not reopen, send an Email to Customer “Thank you. This Ticket was closed. If your ticket was not solved, please open a new ticket by answering this Mail / Clicking this Link / Whatever”. The Customer can decide himself.
To be honest, I’d be happy with that. I don’t want auto reply to open a ticket. Why it isn’t opening it, I’m not sure. It would open tickets in my install until I setup the filters.