Zone AF, just like all 19 point AF mode will focus on the nearest object with decent contrast in the area covered by the AF points (and sometimes even a bit beyond that). So for example if your intended subject is in the upper right corner of the zone area and there is something closer to the camera in the lower left corner of the zone area, it doesn't matter that you want the camera to focus on your subject, the 7D will focus on the closer subject, period. It has to make a decision, it cannot read your mind.
Same with the 19 point AF mode, but results can get even more extreme there due to the much bigger AF coverage area.
Here is a demonstration. My intended target was the pen. AF mode: Zone with the middle 9 points.
Image 1: the wine bottle was closer to me/camera, it was on the right side of the Zone AF area, it doesn't matter that I wanted a nice crisp picture of the pen, the bottle was closer ergo Zone AF focused on that while the pen is obviously out of focus.
Image 2: I just pushed the bottle back a few inches. Zone AF worked exactly as it was designed to work, now it focused on the pen since that was the closest object to the camera with decent contrast, covered by my AF zone area. (Note: the wine bottle is still under the Zone AF area too.)
Now, this is not to say that your 7D wasn't defective, I just wanted to show how Zone AF is designed to work. Which makes sense, the designers had to come up with some kind of auto focus priority and the closest object under the AF zone seems to be the most logical one. Imagine shooting a person in front of a busy background. The AF is designed to pick the person to focus on, which is closer, and not the background which is farther. However, it is possible with a thin depth of field (at wide aperture) that if let's say your subject extends his/her arms towards you it will be the hands that will be in perfect focus and not his/her face since the hands are the closest objects to the camera. It can happen.
I hope this helps.