Double Release Failure on Tow

I'm sure a few people here have practiced it... but I really need to know:

Has it ever actually happened? I mean, has there ever been a bona fide certified, verified example of both release hooks failing in flight? The glider can't release, the glider gives the signal, the tow plane can't release, gives the signal; both aircraft land in formation.

Has anybody ever heard of this actually happening? If so, how did it turn out? What was the proficiency level of the pilots who did this? Did anything get scratched or bent?