BMP thumbs are now auto-generated by GGMax, so, we don't have to deal with, something less to do, better for me; after all, it is just a thumb, and has nothing to do with the final result.
The BMP file is open by Gimp as a DDS file, and it is just the thumbnail background.
I think the BMP extension is just talking to the user it is the thumb and nothing else, and it is DDS because GGMax like GG works best with DDS files, due so, GGMax converts all the non-DDS texture files to DDS, giving it some extra work to GGMax, when own texture files are non_DDS format.
Laptop: Lenovo - Intel(R) Celeron(R) CPU 1005M @ 1.90GHz
OS: Windows 10 (64) - Ram: 4 gb - Hd: 283 gb - Video card: Intel(R) HD Graphics
cpu mark: 10396.6
2d graphics mark: 947.9
3d graphics mark: 8310.9
memory mark 2584.8
Disk mark: 1146.3
Passmark rating: 3662.4