Greetings!
This one is pretty simple: when trying to generate map previews via command line, the --preset arg is not used. I first came across this issue when attempting to generate previews to test my own map generation mod, and initially thought that it didn't work on mod-defined map gen presets. However, it appears to not respect the vanilla/base map gen presets either, which seems like a bug to me either way.
Steps to reproduce: run factorio.exe from command line with the following parameters "--generate-map-preview <path> --preset "Island", which will produce a normal map, not an island.
[0.18.35] Command line: --generate-map-preview doesn't work with --preset
Re: [0.18.35] Command line: --generate-map-preview doesn't work with --preset
Also, using internal names does not seem to make any difference. Neither "island" nor "Island" will produce an island map.
Re: [0.18.35] Command line: --generate-map-preview doesn't work with --preset
Thanks for the report.
Fixed for 0.18.41
Fixed for 0.18.41