NSShiftJISStringEncoding or 2147551745 (why?)

I'm now confused that I have found stringEncoding is set to 2147551745 not to 8 for real Shift_JIS files when testing on MacOSX 10.9.
```
NSString *fileString = [NSString stringWithContentsOfURL:myURLShiftJIS usedEncoding:&stringEncoding error:&theErr];
NSLog(@"used encoding: %lu", (unsigned long)stringEncoding);
// NSShiftJISStringEncoding should be 8 but 2147551745 (why?)
```