Ballista Antiair Bolt vs. Warclaws?

Has anyone had any success using the antiair bolt to dismount people?

Today while hitting Wildcreek the stars aligned and we had a guild ballista handy, fresh from picking off the trebs inside. A soulbeast on his Warclaw got a bit too bold, as they will, and trotted on over so I hit him with a ballista #4. It took roughly a third of the mount's health and did not dismount him. Is this a known issue with the guild ballista or does it extend to all versions?