Not that my vision is good enough to detect a single pixel difference, but I looked and did not see this anywhere that I looked for it.
It could be that the dimensions of an element are interfering, but my guess it is because of a “split”. That is, if something is an odd number of pixels and a CSS rule divides it, the browser decides where to apply the rule. For example, if there is an image 123 pixels in height, and the CSS wants to put it in 50%, the browser can not display the image at 61.5 pixel height but only 61 or 62 pixels. How any given browser might make the decision is a complete mystery to me.
What device and browser are you using when you see this?
EDIT
never mind, zoom it was.