Mine didn;t split because of insufficient room. It seemed as if there was no tacking stiching at all - they came apart without any resistance at all.
Same thing happened to me on one of my pairs. I have owned about 10 different pairs of Mabis, and most were constructed very well. However, this one cotton pair felt very thin and almost paper-like. Put them on for the first time, bent down once, and heard a huge rip right up the back. Luckily I hadn't left the house yet.
I think if you have a pair that hasn't ripped yet through several wears, then you're probably OK. The crappy ones usually rip right away.