It appears that Sergey Dogadin, winner of the richly endowed Joseph Joachim competition, is a student of Boris Kushner, one of the judges. The relationship was not declared on the competition website.
It is made clear in Dogadin’s biography here: In March 2013, Sergei was adopted in solo graduate of the University of Arts in Graz (Austria), Professor – Boris Kushnir.
So did Kushnir vote for his own student to win? And did the other judges know?