This is weird. While posting a question of mine today, I noticed the background "flickering" as I repeatedly typed and removed a space from the markdown for a bullet point.
Without the space after the hyphen on the left, with the space on the right:
Here are some 50x50 excerpts from those images, zoomed and with increased contrast:
And just to clear up any remaining doubt:
The "Dust" on the desert is jumping around compared to the robot and its companion. Looks like two separate images layered over each other, and one of them responding weirdly to the question box.
As I've typed this I've noticed the same "jump" happening when I type spaces, so it's not specific to bullet points.
It's very distracting and annoying, and seems like something that's easy to fix (just merge the layers into one image).
I'm on Google Chrome if that's relevant.