I bought a PB Blaze 1/2W & SuperFlash Light Set the first of March this year the same day I took deliver of my new Trek 520. I mounted the SuperFlash directly to the rear rack in the slot provided. I commute about 100 miles a week so in 5 months I have well over 1800 miles with the rear light mounted in that position.
A week ago I reached down to turn off the light before boarding the train and it fell off in my hand. I hope you can see from the photo that the top edge of the molded frame on the back of the light that accepts the removable clip had failed. I emailed PB customer service and had a new back half and clip in under a week. A simple replacement for free.
I have mounted the rebuilt SuperFlash to the rear light strap that came on my Topeak Rack bag in hopes of the prolonging any furture failure. I think the daily pounding on the direct rack mount was to much. It wouldn't take PB much to redesign a thicker piece across the top of the light.