I assumed the reason why it worked is because once you add the texture in the textures tab via Blender before saving and exporting it, it generates a UV map code and it is included in the 3D model file itself.
Not sure where that idea came from, but no. Open source simply means the users have access to the source code for modification if they want to. Otherwise it has the same potential for file incompatibility, bugs, UI quirks, and other problems faced by conventional software development.
It's the Leeds engine, which is heavily based on RenderWare. It looks like they didn't write it very carefully, they have a bug in their DFF reader which shows that somebody really had no idea what he was doing, I already sent a complaint mail telling them about this idiotic code (which only works coincidentally) but got no response.
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