New tire was plugged! Popped off in transit.
 

On my way to work yesterday morning, I had my driver's front tire rip off fairly cleanly along the rim. As I eased to the side of the road, the tire rolled to rest a foot or so ahead of me. Service manager at Mazda said that the tire has been plugged, but this is a NEW Speed3 that I purchased a few months ago. Now my confidence is shaken. Is it commonly accepted that a new car could be sold with a plugged tire?

I wouldn't think that a plug would have anything to do with the tire ripping off the rim, unless you had a loss of air due to the plug first. If you follow what I am saying.
You wouldn't think that new cars would have tires that have been plugged, but I suppose if it picked up a nail or something at the dealership, they would plug it before they would spend the money on a new tire. But, the tires should still be under warranty right?

No, I'm quite confident that the problem was unrelated to to the plug in the tire, but seeing the plug there was a surprise since the car is brand new. I just hope there aren't any more lurking problems -- this could have been very serious if I had been driving on a busy interstate!

And yes, the tires are covered.

was it plugged from the inside or outside?

It was plugged from the outside. Why?

I just got my Speed3 back. Yay (the rental was a Chevy Aveo, hence my excitement)!

if it was inside they could have just not sealed the tire all the way or something