An amazing number of people have responded to my last blog about the red halo around specular highlights in Kodak CineStill film.
Almost half of the responses referred to optical causes (related to the lens) as the likely cause for the phenomenon. This is not the case. There is nothing wrong with the lens and a lens does not produce these effects (at least not with the colour red).
The majority of responses referred to the special treatment of the CineStill emulsion: there is indeed a removal of the black anti-halation layer below the film base. This removal of the so-called rem-jet layer makes the film suitable for development in normal C41 chemicals (instead of the special ECN-2 chemicals.
The removal of this layer allows the light rays to hit the safety film base and possibly even the black pressure plate of the Leica camera.
Only a few persons (Axel Schwalm gave the most elaborate answer) provided a solution for the obvious question why the colour of the halo is red and not white. It would be white when the cause is a diffusion effect or caused by flare. The logic is that the light rays are reflected from the base and expose again the lowest red sensitive emulsion layer and are then being stopped by the gel interlayer.
See diagram below.



Classical Arri- films also show this behaviour of red halos around specular highlights (often head lamps of cars). So it is not only the removal of the rem-jet that causes the phenomenon.

I wish to thank all respondents for their effort and advices.