Canon 580EX II speedlite: correct exposure

I purchased a Canon 580EX II Speedlite on Saturday, and to be honest I ain't too pleased with it given its high price. I really don't think Canon know how to do flash.

Anyway, the thing that really worries/surprises/irritates me the most is the apparant 1-stop under-exposure across all exposure modes.

I am wondering, do I have a dud copy of the flashgun or is this how the gun is supposed to work by design?

I set my camera up in Manual exposure mode at settings of 1/125, f5.6, ISO200 and was testing indoors during the evening. When I compared shots with my Metz flashgun, I found that the Metz shots were nice and bright/well exposed but the Canon Speedlite always seemed to render an image at around middle grey i.e. around 126 on a histogram. The difference between the Metz shots and those of Canon was around 1 to 1.3 EV. I also have access to other brand's guns (Olympus, Sony) and they too render a brigter image.

So is this new fangled Canon E-TTL/E-TTL II supposed to work that way? Or am I in need of a firmware update or new gun?

Advise and experiences appreciated.

Thanks in advance.