I have been trying to create an image consisting of a single column of pixes (from one image) replicated sideways. (And do the same thing for a horizontal row.)
I first tried using the crop tooj, selecting a narrow crop and entering a small number of pixels in the width box (1, 2 or 3px). Each time, when I completed the crop, the image seemed to disappear. If I then used Document > Resize Document and gave it a full width, Photo just hung. I had to resart my PC to get out of it.
Is this a bug, or a feature.
I solved my original problem by using Filter > Distort > Equations and entering x=w/2 (or y-y/2) which gave the desired result.
John