Material paths in .mm3d format still not work properly in mm3d 1.3.8 in windows. I edit material, set correct path for image, I see it in the preview and in the 3D. When I save the file, close mm3d and reopen it, the texture is missing because it look for image in "c::\some\path" - there are two ":".
How to reproduce bug:
1. Create mm3d model (e.g. C:\Temp\model\box.mm3d)
2. Create rectangle
3. Add material "skin" with texture "C:\Temp2\image.png"
(it has to be in different directory to reproduce bug!)
4. Add rectangle to group "alpha", set texture to "skin"
5. Save it
6. Close mm3d
7. Copy box.mm3d to upper directory (from C:\Temp\model to C:\Temp)
8. Open C:\Temp\box.mm3d
9. Of course, texture image is missing, that is ok. Now we want to fix that. Go to materials, choose material "skin", change it texture to point to "C:\Temp2\image.png". Now you see the texture is ok, also in 3D.
10. Save model
11. Close mm3d
12. Reopen "C:\Temp\box.mm3d" - texture is GONE (because C::\Temp\image2.png is invalid file name).