I tore mine a few years back. I was doing a goofy thing in a rock climbing gym. I had it repaired with a button. 1 year later it was stronger then ever with zero pain. It was such a success, I sort of want to tear the other one now to fix some long running tendentious - okay, not really.
What I learned from the Dr. is this typically happens when the arm is fully extended, like in a deadlift. It's not weight as much as the mechanics. If you are fully extended with just the right angle in the wrist and shoulder, it doesn't take much to tear it.
For guys that tore it doing deadlift's, what it palm up or palm down? For mixed grip, which hand was it?
My theory is, it's not the mixed grip that causes it.