Argent Tournament Quest Chain

The quest The Aspirant's Challenge needed for becoming a champion in the Argent Tournament is bugged. The quest states that you need a lance and a mount, talk to Squire David and defeat an Argent Valian that appears. The Valiant is pretty easy, but after I defeat him the quest doesn't update, and I can't finish it. I found a topic on Argent Tournament from 2010, which stated that everything worked fine, so my guess is that this bug happened after the update. Would appreciate any opinion, advice or possible fix. The realm is Deathwing.