Showcase: https://en.wikipedia.org/wiki/User:Fireattack/thumbnail_bug
The generated 221px width one:
https://upload.wikimedia.org/wikipedia/commons/thumb/a/ac/Higurashi.JPG/221px-Higurashi.JPG
actually has intrinsic size of 220x229px, and are stretched to 221x229px in presentation, which makes it obviously blurry compared to the other three, due to the fact it's not a pixel-to-pixel presentation.
The symptom matches T26763, but the difference is I don't even call the thumbnail by height, I just called it by width.