I just ran into a phenomenon that previously mystified me already, but this time it’s getting in the way of using Retrobatch’s output: I’m downscaling images with Multi Scale and one square image, sized to 2800x2800, turns into 180x179 pixels when sizing to a fixed width of 180. For other widths, the output is nicely squared. I would expect that rounding effects for sizes that aren’t divisible are the same for width and height, but apparently they aren’t always. What gives? 
Thanks so much for reporting this. It was the dumbest of dumb bugs on my part, and really easy to fix, which I’ve done for the next release as well as in the latest builds here: https://flyingmeat.com/download/latest/#retrobatch
You can also enable the “retina friendly” option in the scale settings if you want to wait for the final release.