A common problem for both rowers (I'm a fulltime coach) and cyclists is 'ilio-tibial band' syndrome. Basically the same mechanical aspect of these sports encourages a very tight outer thigh which is then linked in to the type of problem that the OP has. The stronger outer side of the thigh over powers inner part (VMO - vastus medialis) and effectively pulls the knee out of it's natural alignment, thus causing problems.

The cause of any individuals problem may differ (weak VMO/poor muscle activation order, tight glutes, others) but it is a serious problem that can lead to chronic injury.

Solutions: diagnosis of the factors causing it, better technique, stretching, remedial training to restore balance to muscle groups.