I notice you have a method to check the client sided-ness of the world, and right now it looks like you have it to only be client sided for a toggle keybinding. Why not check for a remote world?

i.e.
if (player.worldObj.isRemote) {
PacketHandler.sendPacketToServer(new CustomPacketKeyPressed(keyBinding.keyDescription));
} else {
keyBoundItem.keyPressed(stack, player);
}