On Wed, 25 Jan 2017 22:55:15 +0100, Lars Ingebrigtsen wrote:
> Just binding "C-c" in the article buffer (like other prefixed) led to
> problems in other parts of Emacs somehow, so I've reverted that patch
> and will have to implement it a different way.

Sorry, that is my fault.  How about this patch?

* lisp/gnus/gnus-art.el (gnus-article-describe-bindings):
Ignore summary commands that aren't bound to
gnus-article-read-summary-keys.