This is a small attention to detail in Subterfuge that I found. It is actually possible to see a dormant mine. You think it should be impossible since someone has to own the base in order to turn it into a mine, but if a battle there takes place outside of your sonar the image will appear as dormant.
The most interesting part about it is that they made a separate image with the mine's lights off for the dormant mine. Here's an image of a dormant mine and here is a normal mine.