Well what you've just described is a known issue, not a glitch so to speak. The Trivia Discussion forum won't clear its unread status until you view the actual thread list for the forum itself, even if there were only unread messages in one of the sub-forums. If you click back into the Trivia Discussion forum instead of going straight back to the forum home page, it should clear the unread status for the board.
There is a setting to try to make that an automatic process but it's experimental and comes with a performance hit so I left it off.
There is a setting to try to make that an automatic process but it's experimental and comes with a performance hit so I left it off.