IE7 odd try/catch behavior

error.js

  throwAnError = function () {
    throw new Error('Erroring!');
  }

  window.windowMappedError = throwAnError;

  try {
    throwAnError();
  } catch(e) {
    alert('Caught the global error');
  }

  try {
    // IE7 will not properly throw this error
    windowMappedError();
  } catch(e) {
    alert('Caught the window mapped error');
  }