gcc-4.8-20121028 array bound check

[nat...@t-online.de]

I find this array bound check too hard: 

./compiler/gcc-4.8.0-snap/bin/gcc c1.c -O3 -c -Wall

c1.c: In function ‘main’:
c1.c:15:22: warning: array subscript is above array bounds
[-Warray-bounds]
           if (!ab_pid[index]) 
                      ^

extern unsigned char ab_pid_count,old_rfcb_pid_count; 
extern unsigned short ab_pid[16]; 
extern int found_pid; 

int main()
{
  unsigned char pid_index = 0;
  int index; 

  for (pid_index=0; (pid_index < old_rfcb_pid_count); pid_index++)
    {
      for (index=0; index < ab_pid_count; index++)
        {
          if (!ab_pid[index]) 
            {
              found_pid = 1; 
            }
        };
    }

  return 0; 
}

Does this mean we have to rework the loops like 'index < ab_pid_count &&
index < 16' ? But if so, why does the warning disappear without the
outer loop or with ' unsigned short ab_pid[32]'? 

Regards.