This problem is usually called random overexposure bug/problem, although it's nothing but random and it might quite as well result in underexposure. Perhaps "inaccurate shutter speed problem" would be a better name, because that's what the problem really seems to be, the shutter speed is not always what it should be.

All firmware versions of the D7, including the 7UG, are susceptible to this problem. I haven't yet heard of a single D5 or D7i having this problem. I don't know whether it's a mechanical, electrical (a failing contact inside the camera) or a software problem. Not every camera has it, some have it only occasionally and some have mysteriously recovered by themselves (mine did). It's not a metering problem, it affects manual mode, too.

The problem "kills" a certain aperture value (in the worst case it might "kill" more than just one aperture value). Whenever this aperture value is used, the risk of getting badly exposed photos is high. But that's not all. Focal length is also important - the problem might "jump" one f-stop up or down when you zoom in or out (up, if you zoom in and down if you zoom out). For example, if f/5.6 is giving you trouble at the long end, above 120 mm, you might also get trouble at f/4.5 between 50-120 mm and at f/4.0 below 50 mm focal length.

In my case, fast shutter speeds (faster than 1/125 s) generally resulted in overexposed pictures and slow shutter speeds resulted in underexposed pictures whenever I used "problematic" combinations of aperture and focal length. Looks like the focal length and aperture determine whether there are going to be any problems and the shutter speed determine the final result; overexposure or underexposure. Nothing else, such as ISO, metering mode etc. have any impact.