It appears that if you queue for PVP and a match is found, but then for whatever reason is cancelled and puts you back into searching for a new match, if you zone or change channel it will count as a leaver penalty. This is true even if you manually remove yourself from the searching queue before zoning. So if this happens twice in 20 mins you are locked out even though you manually stopped looking for a match before zoning.
It only seems to happen when you get automatically requeued due to the matchmaking failing the first time. This happens often to sorcs due to the little bit of class balance it tries to do.