Mark, I gather you are using a SiLabs part - unfortunately I have no experience with the i/o configuration of these units. Obviously push-pull refers to the output mode, so how do you select between input and output? Other mcus have a DDR register (data direction register) or suchlike.

The other thing to be aware of is the high input impedance of cmos devices - breathe on a open input and it will change state! You need pullup resistors here - 100k might be a good start. You also only want the interrupt to wake up the cpu, once this is done disable the interrupt and scan the keypad using a timer or whatever method you choose.