The exterior camera on the LEM was basically a miniaturized television camera, all based on state of the art late 60's video technology.
A television camera looking at the lunar surface in full daylight without even the benefit of an atmosphere to diffuse the harsh light will be extremely susceptible to all the foibles of the video camera tubes of the era.
I will attempt to explain my very layperson's understanding of how this ghostly afterimage of bright objects works, but the details of the electronics involved would be a better subject over on the Electrical Engineering board.
Based on what research I've been able to do, the early Vidicon tubes were particularly desirable for television because, though their signal output was low, their signal to noise ratio was also very high so they could be amplified and could therefore operate indoors very well. The downside being that anything that interfered with the signal at the source would also be amplified and show up on the output image.
One cause of this signal interference is heat buildup from bright lights hitting the imaging surface. This heat increases the electrical conductivity of that area of the imaging surface, essentially amplifying the output in that area slightly and causing an afterimage. Letting this go on for a long time can result in damage to the electrical properties and cause burn in on the image.
The camera spent between 17 and 18 minutes between the time Mr. Armstrong descended the ladder until after the famous descent photo was taken and Mr. Aldrin this video takes place. This is more than enough time staring at the lunar surface to build up enough heat for a strong afterimage. Once something blocked the excess light (like, for example, a giant space suit) the surface is able to cool and the afterimage slowly fades away.