Superior Rune of the Guardian
I have similar bug with Superior Rune of the Thief.
I put two runes into 2 of my armor pieces and it shows 8/6.
Same here. I bought 1 rune thinking since I’m a guardian I only needed 1 because all the bonuses were colored blue. However, once I applied it, it showed 7/6 in red and none of the bonuses are applied.
Somebody in another thread said that this is a cosmetic bug associated with including runes in your SPvP gear. If that’s the case for you, too, you might want to specify that to make it easier to track down the issue.