i2C Using IO Pi Plus Only receiving half of the interupts

Question

Morning,

I'm a newb to this, so suspect i'm just doing something silly, or don't quite understand what i have written. Either way... here we go.

I have a Pi with an IO Pi Plus board attached (https://www.abelectronics.co.uk/p/54/io-pi-plus) and am attempting to utilise all the pins in Bus 1 to interface with some buttons i have wired up, from pin to ground.

from __future__ import absolute_import, division, print_function, \
                                                    unicode_literals
import time

try:
    from IOPi import IOPi
except ImportError:
    print("Failed to import IOPi from python system path")
    print("Importing from parent folder instead")
    try:
        import sys
        sys.path.append('..')
        from IOPi import IOPi
    except ImportError:
        raise ImportError(
            "Failed to import library from parent folder")


def main():
    '''
    Main program function
    '''

    busin = IOPi(0x20)

    # Set port 0 on the busin bus to be inputs with internal pull-ups enabled.
    busin.set_port_pullups(0, 0xFF)
    busin.set_port_direction(0, 0xFF)
    # Invert the port so pins will show 1 when grounded
    busin.invert_port(0, 0xFF)
    # Set the interrupts default value for port 0 to 0x00 so the interrupt
    # will trigger when any pin registers as true
    busin.set_interrupt_defaults(0, 0x00)
    # Set the interrupt type to be 1 on each pin for port 0 so an interrupt is
    # fired when the pin matches the default value
    busin.set_interrupt_type(0, 0xFF)
    # Enable interrupts for all pins on port 0
    busin.set_interrupt_on_port(0, 0xFF)
    # Reset the interrupts
    busin.reset_interrupts()

    while True:

        # read the interrupt status for each port.

        if (busin.read_interrupt_status(0) != 0):
            # If the status is not 0 then an interrupt has occured
            # on one of the pins so read the value from the interrupt capture
            value = busin.read_interrupt_capture(0)

            # write the value to port 0 on the busout bus
            print("button pressed: ",  value)
        # sleep 200ms before checking the pin again
        time.sleep(0.2)


if __name__ == "__main__":
    main()

This is the code i am running, now it seems that only pins 1 through 8 seem to give me a response, rather than pins 1 through 16 which is what i had expected. Wondered what i was doing wrong? sorry again, this is my first rodeo with python and the pi..

thanks

Andrew