Issue and comment creation mail handler not working

Summary

Replies or forwards via email are getting into JIRA as new issues instead of comments when there is no issue-key on the subject.

Environment

• Jira 55701f88

Steps to Reproduce

1. Have a "Create a new issue or add comment to an exiting issue" mail handler set.
2. Send an email to that mail handler.
   • JIRA will create a new issue (e.g.: AB-1).
3. Reply or forward that same email to the mail handler; however, ensure that the subject header does not contain the issue key.

Expected Results

JIRA should add a comment to the existing issue as it's a reply/forward to the email.

Actual Results

JIRA creates a new issue.

Notes

The Creating issues and comments from email documentation states that:

Issue and comment creation
The following diagram shows how Jira processes each incoming email message and determines how its content becomes a new issue or a comment on an existing issue:

Workaround

None.