I can now upload maps with custom textures and everybody who downloads the map can see it as intended; however, the remaining problem is that they can not see the map's preview.
If the map uses a custom texture, the map vault apparently creates a blank preview image. Obviously it's hard to get people to join the game when they have no idea what the map looks like.
I think the relevant part of the code is here: https://bitbucket.org/thepilot/modular- ... ult#cl-332
So far as I can tell, it checks if a preview already exists with the file name "mapname.dds" and if so skips manually generating one. The problem is that when I provide a "mapname.dds" file it still won't use it.
Help? I don't want to upload maps to the vault which nobody can preview

PS - Please delete everything I ever uploaded to the map vault as of today (31 march 2013) because all these texture/preview problems means most of them are broken/incomplete. Thanks.