Here is my story with the problems of this lens.
When I first got the sigma85 i noticed that it sufferd from front focusing. I sent it to Sigma service center for calibration. When I got the lens back, it still had problems with front focus!
I tried to correct the problem by using the micro focus adjustment on my 5D Mark II. But it was no good, because the focus problem varied on different distances. I sent the sigma85 back to the service center (again), and when I got it back the 2nd time it was still no good.
I was very frustrated, and then I sent my 5D Mark II to service at Canon, to see if there was something wrong with my camera. They did a full check on the auto focus, adjusted and tweaked it a little bit and sent it back to me. I tried the camera with the sigma85 and the lens was still no good. Front focusing was still a big issue.
BUT, now when I tried to use the micro focus adjustment it worked well on all distances!! It no longer matterd how far or how close i was to the subject. Micro focus gives me perfect focus all the time.
So now I have a front focusing Sigma 85 that works great thanks to micro focus adjustment. Fine with me!