My guess is somehow they did a double powder charge. And frankly I've never been a fan of the Remington Golden Bullets (guessing since you said it was Rem ammo). And with the poor quality of that ammo I've experienced in the past I wouldn't be surprised if that was the case. I'd say it was probably a high charge and a weak spot in the case.
Yeah, I've never had a problem with that stuff, until now... but, needless to say, I won't be buying it again, no matter how cheap it is!