An "idiot scratch" on a 1911 is caused by incorrect re-assembly technique. For some reason lots of people think that the slide stop rotates upward from the trigger area while applying pressure to it in an attempt to push it into place. It doesn't and the result is the "idiot scratch".
The correct way is to line up the takedown notch (crescent cut) in the slide with the slide stop and push the slide stop home. Sometimes they can be quite reluctant but with a little stone work on the back of the slide stop they snick into place quite nicely.