Could you possibly send us any scene where this can be observed, with 3ds Max Bitmaps used? So that we would just open it and convert to CBitmap.
The uploader is in my signature.
According to my simple test:
Empty scene - 660 KB
Max Bitmap - 916 KB
Corona Bitmap - 920 KB
So there is some difference, but negligible for such a simple scene.
Also, there is one thing: when you use the converter script, it will actually duplicate the nodes in the material editor. So you will end up with BOTH Max and Corona Bitmaps stored in the scene. Maybe this is causing the issue?