Why does the server return the values which were passed in? #3257

Just out of curiosity, why does the server return the values which were passed in? If we have to return something, why not return the previous state which we've replaced? That seems more likely to be useful, since the client already knows what it asked for, but it might be good to know what it replaced (e.g., to detect collisions with other, unsynchronized clients...).

Originally posted by @webbnh in #3191 (comment)