run this code on Visual Studio 6 in debug mode
Code:
#include <iostream>
#include <ctype.h>
int main() 
{
  if (isalpha('æ'))
    cout << "this is sad" << endl;
  else
    cout << "okay" << endl;
  cin.get();
  return 0;
}

Various other characters will also return true. Interestingly, in debug mode, isalpha works correctly....