sounds like a cool thing to report to the developers, since the game is in EARLY RELEASE broken mode.
also, if you are playing online, then that is a no no.
Actually I noticed this to when tinkering myself before the trainer was released, especially when playing online. Seems like if you have infinite ammo turned on, it will get to the point where your bullets will do no damage and simply pass through enemies. If you disable the hack and reload the gun, it starts doing damage again. Might be a problem with the game on how it deals with syncing ammo with the server. The server may believe you have no ammo left in the clip while the client still has max ammo in the clip due to the hack.