Global Variable Lost During Interrupt Routine - HC08 Microcontroller

HI All,

weirdest problem. I have a global variable named maxADR which supposed
to hold the value of the last A to D conversion that was greater than
zero, problem is it gets erased after each interrupt routine! Here's
how I'm doing it:

#include <stdio.h>
....

unsigned char maxADR;

....

void main(void){
....
asm CLR;
for (;;){
 //do nothing
}

interrupt 16 void ADC_ISR(void){
  if (maxADR > 1) doLights();

  ...
  if (ADR > 15) maxADR = ADR/15;
  adrval = ADR;
}

funny thing is as soon as the ADR goes to zero, it seems like maxADR
falls below 1 too ! WHY? anyone know why it's losing its value?

Thanks,
Aria