Guild Wars 2

I’m not sure if this is a bug or not. But I googled and searched this forum up and down and looked at the wiki for the answer and found none. I was wondering why I can’t transmute my level 80 Ogdens Mask Soulbound with a Krait rune inside of it? Is it because it is soulbound and I already equipped it?

Basic Trans Stone: 1-79 items.
Fine Trans Stone: Level 80 items.