Okay, I'm dealing with custom designed mecha, and I've been using mechaprize to get them so I can check their stats and PV and such, and I just today noticed that designs that I hadn't set a SDL_Sprite for weren't showing anything in the sprite window when I go to examine them in the field HQ. I'm not 100% certain that it's been happening all along, or if it happens with files other than the ones I wrote, or any of that, but I thought I'd mention it.
They do seem to pull up the default sprite for their type when I go to the worldmap, although Hoverfighters appearantly default to the buruburu sprite like battroids?