Wow, that's a bit different and worse than I was expecting.
How old were these mags when they exploded? Maybe there's some sort of metallurgical issue and the metal becomes weakened from everyday use.
On the other hand, I've always heard that some gas should be left in the magazine when storing it to keep the seals healthy. It's always been my experience that mags that go into storage ungassed tend to develop leaks, where as mags that always have a bit of gas in them almost never develop a leak unless they suffer a hard fall.