Donk Calls

Don't you just love it when you get the donk call? Playing online today, I had a fair chip count and found pocket 8's. My all-in shove was called by small blind with a Jack/five suited. He caught a jack and a 5 on the flop. Go figure. Later, another tournament my JJ shove gets called by A/8 suited. He catches an ace. Why is it that the donk with the hand that catches is the one that calls you?