**facepalm**
I was using Firefox on Mac, and repeatedly saw this image being stretched (squeezed, really). I then switched to safari, no problem. Firefox on a Linux box, no problem. Went back to Firefox on Mac, cleared the browser cache, went back to the page in question – no problem.
Thank you, kind person, for pointing out something I really, really, really should have tried on my own in the first 5 minutes.
