I think I get why some people are saying they should return it. They are thinking of this as if you overpaid at a restaurant or something like that. Peer to peer. Lets say I was paying you for lunch in bitcoin and I accidentally paid you more than you asked for. You could send the excess amount back to me. This is using the system as designed. What is happening here is different. We are talking about a software mistake and we aren't talking about paying person to person. This is built into the protocol. Not to mention the agreement the Pool op has with the miners who seem to have no say in this deal.