Manticorp:
However, when I replace the PORTB = LEDON/LEDOFF; parts of the code above with standard arduino code (digitalWrite(pin,HIGH)) it ceases to work properly...I'm tearing my hair out over here!
Note that writing a value to PORTB will change ALL pins associated with PORTB. It looks like LEDON and LEDOFF are changing two different pins. One of those pins is an input so writing to it is turning the pull-up resistor ON (1) and OFF (0).