Create or Comment Handler will not add CC's email address as watcher if the issue already exist

The email address in CC is not added as Watcher when issue is commented via Email. This problem only occurred when user commenting on the issue and add email address to the CC in the email. Here are the steps to reproduce the problem:

1. create a new service using Create Or Comment handler with the "ccwatcher=true"
2. write a new email, set the CC with a JIRA User's email and send it to the POP/IMAP server. The JIRA User will be added as Watcher to the new issue.
3. create another new issue via email or inside JIRA. Then, write a new email and set the CC with a JIRA User's email and set the newly created Issue Key in the Email's subject. The JIRA User will not be added as Watcher to the issue.