I found an even better reason once. The flaps are retracted by independent springs. So at 300 feet or so after take-off with flap 15, you command flaps up, and only one retracts. The aircraft remains controllable in that state, but it's not my choice of configuration on a high-workload departure. (BTW, solution is to extend flap to 15 again, reduce airspeed, and retract again.)
Your way to solve the problem is correct but in order to prevent it from re-ocurring replace the flap rollers to the plastic type, available from Tony Brown, Webco and Piper. If you replaced them and the problem persist clean the tracks and make sure that they are not lubricated, keep them dry.