Looks like we have a definite consensus on this coin...I agree with AU and cleaning.. Disclosure: this coin came part of an inherited collection. The coin was in a bezel. I liberated it by using a dremel tool with a diamond blade to break the tabs from the back. It was a very delicate operation, but the coin was not touched. I think the coin was cleaned as well, since it was in a bezel and used as jewelry.
Great observation..I didn't see this before you mentioned it..kinda proves the coin has been cleaned.