That happens to me several times a year. I think it has to do with where in the drift you fish. Ive hooked up this way whe I'm in a rock garden that has a pretty good flow to it I free spool through the tail out area behind a rock. I believe once you start to free spool you have minor separation between the hook and corkie and the fish hits the corkie while the hook dangles slightly under it. You set the hook or in your case just hang on and the hook is lodged under it's jaw. Right or wrong thats been my thoughts on this over the years.