Bill posed the question: Was this intended as part of the design?
Answer: "No"; the model had plain (dark) background. The image is from Stamp Auction Network, Brigham Auction #5. Link can't be posted because I have <50 posts.
The engraver interprets the background in the form of lines/cross hatch or combo of both; see second image; the break in the lines is un-usual.
Hope this helps.