I created a forum [Input Devices] whose parent was (root node). When I added a child [Keyboard], it did not display as a sub-forum, but directly underneath as a separate forum:
When I changed the parent of [Input Devices] to a category (whose parent was root node), the child [Keyboard] correctly displayed as a sub-forum.
Parent: Testing Category (category is at root node level)
Is it a requirement to have forums underneath a category for the subs to display correctly, or is this a bug/oversight?