Weapon Lock doesn't do that, it prevents you from picking up weapons which will replace your existing weapon (it "locks" you to your current "weapon"!). It sounds like you have some kind of rogue input. Maybe a gamepad that's laying under your desk with a button pressed? Although if he doesn't start throwing until you hit a button, that's not it. Or accessibility features - I believe there is a windows feature that will make CTRL and SHIFT be toggles instead of holds. Whatever the cause, I'd start by going into key config and changing the key for weapons to something else and see if that resolves it.