well.. they bash against the bushings going forward as well.. and they are circular... so I take baxtefer's point to some degree

(why do I get that can-of-worms-opening type feeling....)

My line of thinking is that more sudden staccato like movement of say, a heavier, guy like myself (just shy of 105kg or ~230lb) practising his trackstands with lots of rapid, to and fro movement might have also placed undue stress and weakened the chain as well.