Riding Mount wont work, it mounts then dissapears

Hi,

I started a gnome, and recently when I try to use my level 20 mount it wont let me ride it.

I press the button, it casts the spell then after its done casting it immediately dismounts.

anyone know why

Because you are using the HD client. Use the regular client instead.

i can use my mount on other characters, this gnome is the only one that is having the issue

Yes, the bug only affects gnomes.