Game port
This can be fixed by using pins and input meant for the second joystick (i.e. button 5 through 8 are mapped to the signals to the axis pins meant for the second joystick - resulting in the issue of the two buttons mapped to the same axis being not both usable at the same time), using some normally "unused" pins, or changing the joystick's circuits (and related software) to read a 4-bit state code from the four button inputs, thus giving up to 16 button combinations (though with some limitations e.g. some buttons may not be held down) or a combination of both techniques.