Admittedly, my comment refers to early days some years ago when the fleet was older, and doubtless smaller, but the incidents are there in the AAIB Bulletins. As RATBOY says, we have a choice as to who gets our money, and j-class' experience doesn't convince me to use them.
Nobody has answered if the downgrading leads to refunds? I know it does with BA: when I got bounced from business class on AA, they rerouted me 1st Class all the way from LAX to LHR, paid for a meal, and gave me a cash voucher.