This bug occured when I had open an image with a resolution of 766 px by 10 px, and I was working in the typical 8-bit RGB colorspace. I had the pixel grid enabled, and I was zoomed in at 4853.72%. I opened the Color Range selection tool, and when the selection preview was set to "Grayscale", an extra row of the pixel grid appeared underneath the image, without a bottom edge. None of the other selection preview options engender this visual error.
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