Rascal,
Thanks for posting. I only collect Newfoundland since 1968 and know this stamp pretty well. It is not a known variety sadly, as YakBoomer notes above. Still its a great little stamp, and the cancel is pretty and the margins are excellent. My guess on the "freak" aspect is either as you hypothesize or it could be damage down the road (like a hinge or sticker or some damage)..it appears to have other surface damage on the UL and far right.
Still, a pretty stamp.
It may interest you to know that this 1890 stamp has no watermark, its earliest known use seen is October of 1893 and there a mind dizzing number of color varieties (at least 6 in the catalog, perhaps more) not including 5 color proofs (brown, violet, blue, green, vermillion imperforates).
Here is my page so you can see some of the color varieties--all perf 12 x 12.
