I'm getting some good rates from Toronto direct to Malaga for this time frame. The week before and the week after these dates, the prices are up again. Is there something special or good about travelling Sept 6 - 20 in Spain?
Maybe nobody wants to fly September 11 (Remember what happened on 9/11 2001). It might also be because peak tourist season prices (at Hotels, etc.) are still in effect. The latter is not the case for after 20 Sept: Maybe there's a Golf thing happening at Valderrama ...