My 2008 CAAD9 6 had 130 miles on it when the rear derailleur pulled a suicide maneuver into my rear wheel. Junked the frame, rear wheel, and half the drive train. The limit screws were properly set, hanger and derailleur straight as a whistle, and no apparent funny business in the chain. I wasn't shifting, and was in the middle of the cassette when the rear derailleur got caught. Freaky accidents do happen.