Similar problems with the rear brake locking up can occur if there's not sufficient free-play above normal resting position if the brake fluid boils and expands - it has to go somewhere and if the pedal can't move, then the pistons will, clamping down on rear disc.
Exactly....a sticky pedal reduces the free-play.
I see them as related because if the brake was dragging it was generating heat....boiling the fluid...makes the brakes lock a lot easier. Combined with the reduced lever travel it caused a problem in my case. They locked a lot easier than they should have.
Long and short of it is the fluid didn't have enough pressure to return the pedal in my case. Result was a dragging brake that locked.
Not arguing your points. Is it redundant? Yes. Unecessary? If everything is functioning properly it is. But that doesn't mean it doesn't serve a purpose. Or it doesn't work.
In short millions of bikes have a return spring. It doesn't hurt anything.
