I had quite a few interesting experiences when working at the university hospital as scientific programmer for the image processing system we had developed. This was a DOS system with monochrome text monitor, equipped with a frame grabber and an extra colour monitor to show the image from the camera and ant processed image. One day a user came to complain that since my last software update, the mouse was behaving in reverse: move left, the cursor goes right, move up, the cursor goes down, etc. I explained that I had not changed anything in the mouse-handling, but agreed to come and have a look. It turned out she was holding the mouse with the "tail end" facing her. After rotating the rodent 180 degrees I invited her to try again. Rather red-faced, she went to work.
Five minutes later she comes into my office complaining that the image was upside-down (again blaming the software upgrade). Completely baffled at this, I went and had a look. I found everything looked normal (all text readable without putting a crick in your neck). I suggested all looked well. She then said that it was the colour image on the monitor which was upside-down. This image just showed some bacteria, which looked much the same in any orientation. The text on that screen also looked fine. I asked her again what the problem was, and finally it dawned on me. I went to the microscope, rotated the camera (which she had mounted) by 180 degrees, and asked her if this was better. Very red-faced, she went back to work.
I think she would not have dared come to complain about anything that month, even if the system had caught fire.