[Kevin Sevcik]

I think you have to read the entire port to be able to clear the flag, but reading a single pin might work. What happens is if you don't clear the mismatch by reading the entire port, or maybe reading one pin, is the flag continues to be set over and over, and you'll keep jumping back into your ISR. So if you try your way and get a red light of death, you'll know why.

Second point. Your method works if you only care about 0 to 1 transitions on the pin. 1 to 0 transitions will still cause interrupts and you'll still have to service them, however. So using interrupts 3-6 when you only care about 0 to 1 transitions is pretty wasteful of your resources and you'll only be able to service half as many interrupts as you'd other wise be able to.