Drupal Forum vocabulary 'required' value not active with TSS

I'll try and communicate the issue I am experiencing.

Associated with my 'Forum topic' content type are two taxonomy term lists. One is the forum vocabularies and one is a simple taxonomy list. It seems that Drupal's forum vocabulary list is, by default, required, which makes sense. You also do not have access to setting this when editing the list of forum vocabularies through /admin/content/taxonomy/edit/vocabulary/1, which also makes sense.

When I turn on the TSS for both fields, only the simple taxonomy list, displays and behaves like it is a required field (when that value has been selected). The forum vocabulary list, on the other hand, does not display or act like a required field. I'm fairly certain that the disabled 'required' value is happening with TSS, since when I deselect TSS for that forum vocabulary the required value comes back. Anyone else having this issue or any suggestions on how I can get this feature working like it is designed to work in Drupal core?

thanks