I just had a report from a gnome maintainer in Debian about that. It seems that, when an app ship a .desktop file containing a command using pkexec (for example gnome-system-log which has: Exec=pkexec gnome-system-log), the app won't run (either from panel menu or from desktop menu) and .xsession-errors has:
Refusing to render service to dead parents.
Created attachment 5254
Fix the double forking
Pushed to master (although sadly I forgot to put Colin's name in as the commit author):
Author: Jannis Pohlmann <email@example.com>
Date: Sun Jul 27 16:25:57 2014 +0200
Avoid double forking when spawning external apps (bug #9373)
Some security conscious applications such as pkexec detect double forks
and refuse to operate. Avoiding the double fork here is very simple.
Thanks for that, and no worries about authorship :)