Well, pfranks, I can only point again to check this with the support, or the manual. I can’t change the application’s behavior. Note that the manual refers to the material, not to textures.
Since Autodesk is the last known owner of the app (Alias | Wavefront), I wrote to them for a White Paper. If I get a reply from them, I will share the information of course.
All the best
No idea how valid this is…
The extension definitions [suffix] seems questionable, and perhaps lead even to more problems.
Materials and texture paths in OBJ format will be defined in a separate file (*.mtl). Use this setting to define if and how materials should be exported. Only UV projections will be exported. Since the OBJ and Cinema 4D material systems cannot be transferred to one another loss-free, it is often sufficient to export only material assignments (but not the material itself) using the Export Name and Default option and then replace the materials in the application used to render the scene with better/adapted materials.
The following options are available:
No *.mtl file will be exported.
Export Name and Default
All existing material assignments will be maintained and the materials themselves will be replaced by preset materials (either White or Random Colors, as defined in the Default Material setting)
If this option is selected, selected materials and those assigned to polygonal objects will be “translated” and exported as defined in Cinema 4D.
it’s always recommended not to use spaces in bitmap names. Other applications can experience problems when importing these files.