I think that is caused from over tightening the frame to bezel screws. I juts looked at 4 I have here and none are like that and the two installed in the cars aren't either.
I know this is correct.
I warn my customers to not over tighten those bezel to housing screws.
I have pics here that show outline of the housings perimeter in the plastic.
I'm guessing the dimples have been there a long time and only more visible due to new paint.
