It's possible to swing the long hafted blade from horseback. This is clearly a glitch, and it has a glitched animation. In fact, I'm pretty sure that it would be physically impossible to swing a weapon like that from horseback. Not to mention that with 153 length it's ridiculously long compared to all other weapons that you can swing from horseback.
Remove the swings with this weapon. Make it thrust only on horseback like all the other polearms.