I think that before people comment they should really understand the implication here.
In games, there's some stuff done client side, some stuff done server-side, and some stuff done server-side that's predicted in the client.
In modern games, when you're in a multiplayer match and you see another player, then aim and shoot, what happens is that your client will "predict" what's supposed to happen: reducing your ammo count by one, causing damage to the opponent (blood splatter, etc) and your client tells the server "i am here, and i hit this guy when he was here"
The server then figures out if that's "valid" by looking at it's version of the game state- as the server it should have the "real" version of said state and then sends updates to everyone as to how that state has changed. Note, that in modern predictive games this doesn't always mean that person A could shoot person B now, just that they could have X amount of time in the past based on that player's lag. There are ways to exploit this in massive lag scenarios but there's ways to fix that.
Note that this all still has the players' 'real' positions and ammo counts and health totals on the server. The client makes guesses as to what they are going to be, but defers to the server when the server updates them in such a way that's inaccurate.
Now, what happens if the *client* gets to decide everything? What if the client tells the server what position you're in, and the server decides that's true without verifying it? It just updates it's local (and everyone else's) gamestate that says you are in position x,y,z. This is how location hacks in World of Warcraft work- it's one of the things that the client has authority on. Note that you can't actually hack your inventory in WoW- you can hack your location to teleport to mining nodes but you can't just give yourself more minerals.
Now what if
a) *everything* was on the client
b) the server isn't even equipped to 'verify' any data.
c) the client can be externally changed and then update the server with that information? This is the part that makes me worried- CONSOLE games tend not to care as much bout this and can even go player-to-player with no server, because the ability to hack a networked modern console usually lower then the ability to do so on PC which is completey open.
Not saying all of this is true, mind you, but if it is, fixing it s a huge, major change in the network backend and rushing it out is only going to result in a buggy, unplayable mess. after all,you're going entirely from a system where game state data is player client based to one that's server based for all players, and the network overhead therein would be a difficult hurdle as well.
Now it's possible this was a testing switch that got left on and the game does support server validation. Hopefully that's the case.