Here is the reply I got from Impossible:
"We have heard about the fading-problem. Unfortunately we cannot give a proper explenation why this is happening, as every film seems to show different reactions. We know, that the chemicals still react days after exposing, so the best way to handle the images, ist to store them in a dark and cool place, after exposing. We are currently trying to improve the film, hopefully the final edition will not show any fading problem."