I noticed this bug back in Alpha and tested it last night and it still works.
Let’s say you spec into forge guard, get molten blade and forge strike, place them on your hotkey bar and then respec out of forge guard and into voidknight or paladin. You’ll keep those skills on your hotbar and can use them! Only if you take them off hotbar do they disapear. It was funny being a lv70 voidknight spamming molten blade and forge strike!