Oop - nope, this is not the case - this is Windows, my laptop video settings are set to scale 150% by default. If I reset this to 100%, it displays normally.
It looks strange because my image editor does NOT scale the images - it shows an image zoomed at 100% to be what I expect, but not when you view the image on the forums.
Similarly, the Windows photo viewer also displays it at what looks like normal size, not zoomed.