Can't use Warden Toy with Ash'adar Mount

I just received the Ash’adar, Harbringer of Dawn mount and it looks as though it is a warden mount, so I tried to use the Sira’s Extra Cloak in my toy box and the appearance does not stick when I am mounted. Once I am off my mount, the form will appear. It doesn’t add up on why this appearance won’t work while on this mount. It would have matched well together, and other appearances work, such as Dark Ranger.