This bug was reported by a static analyzer run against the Chromium browser, which uses libxml2, with the downstream bug at http://code.google.com/p/chromium/issues/detail?id=84132

The following is the original error report:

V501 There are identical sub-expressions 'sub->negNsSet->value' to the left and to the right of the '==' operator. libxml xmlschemas.c 13949

static int
xmlSchemaCheckCOSNSSubset(...)
{
  ...
  if ((sub->negNsSet != NULL) &&
      (super->negNsSet != NULL) &&
      (sub->negNsSet->value == sub->negNsSet->value))
   return 0;
 ...
}


The correct check should be:
  if ((sub->negNsSet != NULL) &&
      (super->negNsSet != NULL) &&
      (sub->negNsSet->value == super->negNsSet->value))
   return 0;