How's this for a house rule??

I'm not sure you can say this ruling is correct. I've been called to rule in this situation and if players not involved in the hand can verify that they saw the winning hand face up on the table then that player is getting the pot. I don't care whose cards are mucked, it is the casino's job to see that the pot gets pushed to the winning hand.

Cards speak and everyone at the table is jointly responsible to see that pots are correctly awarded.