Why i can't add the discussion boards of some fellowships to my favourite boards?

For example i can't add discussion board of "The Gothic Chess Ladder: Enter the Vortex" or "Debate club" to the list of my favourite boards, while i can add the discussion board of "The Chess Club" for example to my favourite discussion boards.

While the "button" that says add this to favourite board, appers at The Chess Club fellowship, it doesn't appear at the other......