I too was thinking it could have happened when they were cutting it, but it really doesn't look that way under magnification and there is nothing apparent on the other side. It just looks like part of the original design. It certainly appears under magnification that the low spots of the design are the same height as the rest of the background surface and the higher spots rise above the background. Will try cob section eventually. I'm pretty sure we already know what it is, just why does it look so different?
Thanks