Steps to replicate the issue (include links if applicable):

• Go to File:Flag of the Company of Scotland Trading to Africa and the Indies.svg on Commons
• See the bottom pixel line on the 320p, 640p, 1024p, 1280p, and 2560p PNG previews

What happens?:
The bottom line of pixels contain colour values from outside the viewbox (e.g. the yellow from the sun image). This may be because the aspect ratio of the SVG does not match the aspect ratio of the renders – if so, it might be worth effectively setting the vertical resolution to match the viewbox, and then discarding the factions of each pixel on either side of the image (effectively slightly cropping the sides of the image to match the preview resolution), or treating all colour values outside the viewbox as 100% transparency when rendering, if including the entire image is considered preferable.

What should have happened instead?:
No colour values from outside the viewbox should be present. N. B. unlike all the preview resolutions listed above, the 750p preview render does not have the same issue, so whatever settings are applied to it might fix the other resolution previews.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):
I've checked the original SVG in several webbrowsers, inkscape, etc., expecting that the viewbox was incorrectly set, but these pixels do seem to be from fully outside the viewbox.