(sound of hand slapping forehead). I will retract my statement about the bracket not holding its position. I took another look at my PB SF installation and figured out I had the shim positioned incorrectly. The rubber strip needs to wrap in the opposite direction of the bracket clamp; ie the gap between the shim ends needs to be on the "front" of the seatpost. Then as the bracket is tightened, the tabs don't pull in together as much, and the light assembly stays put...