Exposure Bias in Metadata HUD

OK, dumb question #1.

I've been experimenting with exposure settings,
under, exact and over by a couple of stops - but
nothing that is over exposed is ever reflected in the
metadata, and almost all of the under exposed shots
are the same - they show 0ev. I've had some show up
with -0.3ev, but only a few.
The camera is a Canon 20D

I have been doing the experimenting on the camera,
setting various exposures both under and over 1/3 and
2/3 of a stop - but Aperture shows them as having the
same exposure bias. The shutter speed varies when I
change the exposure level course, and that is
reflected in Aperture, but the exposure bias isn't.