[belorn]

This is no different as if the master license text had a "comments" section which said that the license was only for non-commercial use. This has happened many times before, and the legal consensus for it as been more or less the same: The work is under a inconsistent license.

What happen if a person download Shen from a redistributor who had only included source files and no master license file? Can that person then write changes under GPL without being under threat from copyright violations? What if distribution like debian got a GPL package that depend (i.e. links) on Shen?

A lawyer would ask a simple question: What is the authors intention with the license? If it is "changes can be under any license except GPL", then it do not matter if its the authors interpretation of copyright or an explicit license requirement. If the intention is "no changes which is licensed under GPL", then that is the wishes of the author and the legal requirement a distributor has to follow.