I've been using the pro-race tyres for ages and the only problem I've had is the 20c's seem a tad twitchy on the handling but that may be something related just to my bike set up.
As for blow outs or even punctures these are very far and few between on the michelins I've had, nearly every one I've had to replace has been due to regular tyre wear.
I'm just wondering, shot in the dark really but if it's a failure occuring specificly across the tyre whether they've been stored badly as they're folded it's weakened across the tyre on the fold where something heavy may have been placed on top, as I say just a shot in the dark really.