[Leica] 28mm Summicron + M8 on Auto = Overexposure?

[rbaron at concentric.net (Robert D. Baron)]

I've been trying to decide what and why is going on here.  The 28mm
Summicron, when used on my M8 set on automatic, is slightly
overexposing the "frame".

See http://www.bobbaron.com/28CronOct09/index.html .

The first frame is out of the camera at ISO 320, -1/3 EV (stop)
exposure.  It is washed out.  The second frame is the same image
adjusted down another half stop in Lightroom and is a lot closer to
what a correct exposure should be.

Do wider lenses throw the metering off somehow?

I can take some of the pain out of this obviously by setting the
camera to expose at -2/3 rather than -1/3 when I use this lens, but
I'm just curious as to what is going on.

The lens is pretty nice; the third frame is a 100% crop (also iso 320)
with a little more tweaking in Lightroom.

--Bob