OK so it sounds like a bit of a problem.

To rule out angle of view differences, you could try both with the 28mm - unscrew it (and set the lens switch to Manual) so you use the same lens to do both tests...

For what it's worth, when I tried this Full aperture metering gives two stops overexposure, and Stopdown metering gives one stop overexposure on mine, compared to Sekonic spotmeter...