AF points out of focus - why?

I try to understand how AFocusing works – unfortunately very often the results are unpredictable for me. Please take a look at this pictures. My 5D MIII, FL 200mm, Metering Mode: Evaluate, AF Mode: AI Servo AF, AF area: Zone – all as listed on the right site of picture. On picture I have two subjects, in different distance. On subject – a boy – is in focus, other subject – a girl is out of focus. Using ImageBrowser EX I can display AF points – as on my picture. Now my question: Why may subject which supposed to be in focus – red AF points, is in fact out of focus. Why my subject which supposed to be out of focus is in fact in focus. As a zone I had AF point expansion – 9 – in the center of view.
Can you help me to understand that?
Thx in advance

I think its the area set to zone. If you will analyze the photo, the came from direction right in front of the girl in a running motion (to what I see). I experience this a lot too and this is what I assume. The camera focused the boy while he was still in front of the girl (where lights are on), by the time the shutter is pressed, he is on that location already. The Ai Servo is limited to its area assigned to focus, so to what I think, it did not follow your subject to the right.

It could also be front focusing though.. I am not an expert and I would not mind being corrected by others.

My guess would be that it is down to your AI servo settings and how you are using the camera to focus. You most likely held down the shutter release to AF as the boy was in front of those focus points or were already tracking him and then decided to begin tracking the girl and your tracking sensitivity was not fast enough. There are many other factors as well, but I can almost assure you it won't be an issue with the camera or lens. It will be user error and/or incorrect AF settings.

I highly suggest reading this: http://cpn.canon-europe.com …rkIII_eng_Janua​ry2013.pdf

AI Servo... the camera locked onto the boy as he ran in front of the active AF points, and the camera has proceeded to track his movement rather than the person behind.
Now this is usually what you want the AF system to do, as for example when shooting sports it can be very frustrating if the camera decides to focus on the background or audience rather than the players.

You should change the AF mode to Case 2 as this will tell the 5D3 to be aware that it should ignore obstacles entering the frame.

You in the wrong case or you released the focus button after focusing on boy and before hitting shutter on girl.

Agreed. You were tracking the boy and fired the shutter just as he moved out of the way of the girl. The camera is operating properly.

Or, your priority is set to "Shutter" instead of "Focus"...

The AF locked onto the boy in he foreground. The girl in the background is less sharp because of the shallow depth of field.

What did you lock focus on before you hit the trigger? Did AF focus lock on the girl? Both subjects are moving so, it's hard to say what the real problem is unless we know more.

Looking at the pic, it's logical to assume that AF locked on the boy but he moved.

However, I've had similar AF issue with my 5Dc which warranted an AF unit change. It happened when my shutter count was at 16k.

From the exif data at the image, it's pretty clear.
You are using zone AF, which in this case is limited to the center. That's fine, if it's the girl in the background you want in focus.
You are using Servo AF, so focus will change and try to track whatever comes into the zone.
But you are using a tracking sensitivity of 0. That translates to a delay of about half a second before the camera will let go from focusing on the boy who for a while blocked sight of the girl. Thus focus will "hang" at the distance to the boy for a short time, before the camera refocuses. If you had taken a few more images, focus would have shifted after about half a second.

I like to thank you to all of you.
All comments are very valuable for me.
All your comments shows me that AF is not simple as I expected. There is so many factors to thing about before take a shot. I'll study this dipper, and perhaps I will be back with questions.
Thanks to all of you

The 5D Mark III has a state of the art AF system from the 1DX which is designed for sports professionals... it is extremely complicated but they've simplified the UI as much as possible.

For children I use AI Servo with AF configuration Case 3.
Works pretty well with their erratic motion too.