Subscriptions and email logging

Excellent product. I have a question around subscriptions and email logging.

I have a system that is working version 1.1-beta2. email in and out etc... We are in the process of testing and I'm not sure if I have missed something.

We accept messages from external users, enabled Send responses when issues are created and Subscribe senders to created issues from the sending email section.

This is what happens
External User emails in with an issue
It creates the issue within the system
External User gets an email stating it has been created and how to responded (i.e. Include [#ref] in the subject line)

My issue is when the admin or a internal user adds a comment, file etc to the issue. The External users gets an update but the subject does not contain the issue ID so when they respond (which end users do) a NEW issue is created.

Is there a way to include the issue ID in all emails sent so the can be responded to without having to add the issue ID.

Thanks