weird loop bug

Both variants of the below code fail:

int main()
{
   i = 1;
   while ( _gt_SxS_(i, 0) ) {
#if 1
       i = _add_SxS_(i,1);
#else
       i = _mul_SxS_(2,i);
#endif
   }
   return i;
}

sac2c -noprelude using sac2c 2.0.0-Tintigny-181-ge8f88 yields:

a return value of 2 in the addition version

a non-terminating program in the multiplication version