Forum topics count twice when assigned to group

When adding a forum topic to a group... if the "Public" checkbox is also checked, you will see +1 topics in the forum listing where the number of your forum topics is printed. Even though that number of topics does not exist.

Attached image suggests that when checking a group, the "Public" checkbox UN-checks and disables automatically. That would prevent the issue from presenting itself. The next step would be that if un-checking all groups (un-assigning the topic) the "Public" checkbox re-check itself. If that kind of thing is warranted.

Apologies if this is a duplicate issue.