Can't be sure whether this is a bug or an error. As I see, the "Regular" and "Small" settings have worked well all right. Nonetheless, if I set the thumbnail size to "Large", images with less than four hundred horizontal pixels, especially non-free ones, would be enlarged. Even images using upright scale doesn't prevent such enlargement.

Example(s):

• https://en.wikipedia.org/wiki/Ain%27t_Nobody
• https://en.wikipedia.org/wiki/Hallelujah_(Leonard_Cohen_song)

Other related tasks (unsure whether this task is a duplicate of one of the tasks): T424910, T421524