Administrators cannot control their own group memberships

Steps to reproduce:

1. Login as administrators in Confluence only OnDemand instance
2. Go to "Confluence Admin -> Users"
3. Click on current username used and then, Edit Groups
4. Tick on any other group listed to join the group
5. Click Save and below error will be thrown:

   To prevent Confluence being left without any administrators, you cannot remove yourself from the last remaining group(s) that allow you to ADMINISTER or USE confluence. If you wish to revoke your administrator access, have another administrator remove you.

Expected Result:

The error shouldn't be thrown if the admin is not trying to leave administrators group but just join other group.
Administrators should be able to join and leave any other group except administrators group.

Actual Result:

Administrators cannot join or leave any group if they try to edit their own memberships.

Notes:

This only affect Confluence only OnDemand. Not JIRA+Confluence as the user management will be controlled by JIRA.

Workaround:

Atlassian Support can work around this by ticking any other wanted groups plus system-administrators group. Save it.

Even though there will an error thrown about joining sysadmin group, the other ticks will be save correctly. Triggering different error seems to get the bug ignored.