Users automatically being created when using non-ABP license

Whenever you setup a Mail Handler in Service Desk using a non-ABP license, users are automatically created by the Mail Handler. This cannot be disabled in the UI while using this license.

1. Setup JIRA. You can configure this JIRA instance to be Public or Private - it doesn't matter.
2. Install JIRA Service Desk using a pre-ABP license. You will continue to use this license.
3. Create a Service Desk Mail Handler in the email channel for Service Desk.
4. E-Mail the account that this Mail Handler uses.

Expected result:
If the email address is not recognized by the JIRA Server, new user and new request should not be created.

Actual result:
If the email address is not recognized by the JIRA Server, the user will be created on the JIRA Server. This user will be assigned to the JIRA User's group, as well as any other groups with JIRA User's Global Permission. This user will occupy a JIRA license.
Even if the JIRA Server is set to "Private", users will be created. This is only while using a pre-ABP license, so the SD isn't Public (there isn't an option to make it Public in pre-ABP licensed SD's).

Workaround at this point:

The only way to turn this off is to install an ABP license, and at that point you get the option to turn off Public Sign up. If Public Sign up is turned off, you finally get the error in the email processing log in Service Desk "Signup is not currently available". New users are finally no longer created. However, if you revert back to the old pre-ABP license, users will start being created again.