Artifacts...
Heh. If I had Google's dough, I would have a less buggy product.
Think about it. Draw the figure by starting at 6 o'clock, proceed straight up to 12, thence to 9, thence toward 3 o'clock. Now veer up northeast and come down exactly where your vertical meets your horizontal.
That doesn't seem like a pattern your graphics program can't help but execute.
I searched for explanations online, didn't find any. Which is Google's raison d'etre, helping you find answers. :(
It could be an “Easter Egg”?