Okay, that seems to do the trick.
I was really confused about the difference of output between Blender and Panda3D. It seems like in Blender the (realtime) shading algorithm is very different to the one used in Panda3D.
Do you know which shading algorithm should I choose in Blender for Diffuse and Specular to get the end result as close to Panda3D as possible?
Now I still have the problem of the Simple -method not working for texture export. Of course, the Bake method always works (bcs the output textures are rendered by Blender Render), but I think it would be cool if somebody could figure out why the Simple -method does not work with this particular model.