7D erratic focus

Hi guys,

I bought a 7D about three months ago to replace my 50D. I decided on the 7D mostly because of the focus system and the better low light abilities. From the get go I had some real focus difficulty, and at first I put it down to myself having to get to know the system. But three months on I'm convinced there's something wrong.

I was just going to have it swapped out, but my local shop is out of stock and Canon can't tell them when they'll have new stock (issues in Japan, I guess), so I'm stuck.

Lenses:

Canon EF 24-105mm f/4 L IS USM
Canon EF 50mm f/1.8 II
Canon EF 200mm f/2.8 L II USM
Sigma 30mm f/1.4 EX DC HSM

Problem:

About 20-30% of shots are completely out of focus. It breaks down as follows:

a) About two thirds are front focussed. The viewfinder shows focus points on the subject lighting up, looking at the image afterwards show the active focus points in the right place, but the focus is off. It is noticably worse in artificial light (even in good artificial light).

b) About a thrid are severely back-focused, often by several meters. In the back-focus issues I notice that the camera does not obey the Canon method of focusing on the nearest subject.

c) In low light situations, the camera often refuses to focus. These re situations where the 50D (and 40D before that) never failed.

The issues are more pronounced on the 50mm f/1.8 and 30mm f/1.4, probably because I tend to use them when I need the speed (otherwise the 24-105L is always on my camera) and tend to shoot them closer to, but seldom completely wide open, so I guess DOF masks things on the smaller apertures.

None of these lenses had focus problems on the 50D and 40D before, and none of them needed MFA. I'm not used to getting mis-focussed shots. I have spent the time and effort to get to know the AF systems in my cameras to know how they behave, and when I get miss-focussed shots, I can always attribute it to my own mistakes. But this is different.

Some samples, straight out of the camera. None of them used focus-recompose (I seldom do). Front focus:

And crops of the focus and in-focus areas:

Back focus:

Has anyone here experienced the same problems? Am I correct in thinking this body is faulty?

I just found there's a firmware update 1.2.5 (I had 1.2.3). It doesn't list anything to do with focus, but since I can't find any information about 1.2.4 I thought it worth doing. I'll spend some more time working on MFA but I'm not hopeful, since it's not consistent front-focus or consistent back-focus.

Thanks
--k