Mods listed as "Class item" mods (i.e.: not titan mark, hunter cloak, or warlock band) can't actually be applied to anything for any class. They simply do not work. I'm hanging onto them in case it gets fixed, but it sucks when you purchase random blue mods from Banshee to get enough for making a legendary mod and the ones you get don't even work (and breaking them down is a diminishing return).