I've had two bad incidents with my MEC panniers. First time, one of the stupid long straps got tangled up in my rear derailleur...while I was riding. And it was night.
Second incident was yesterday, I was about to leave when I realized my rear wheel wasn't turning. I thought the rear brake needed to be fiddled with, I fiddled, didn't make the wheel work. Then I noticed one of the straps I neglected to snap shut was twisted all the way around my rear wheel, behind the plastic ring. Also, the #%#$%#$% buckle was stuck in my spokes. I got out my Swiss Army Knife and cut the strap off (couldn't get it out otherwise) then i kicked the wall beside me, then I punched the wall.
After much swearing, I finally got the strap out of the wheel, and removed the buckle without damaging my spokes. I was not amused.
I'm probably going to take the panniers to MEC today, which I should have done months ago and tell them what happened. What if that strap had done that while I was riding?