Hello,
thx for the hint pjnsmb. We have figured out the facts:
Our upstream, the debian cinnamon team, seems to be busy with preparing the upcoming cinnamon 2.6. Most likely the neccessary changes for coexistence with gnome 3.16 will only be applied in cinnamon 2.6.
For the time being with cinnamon 2.2 in unstable agaida has prepared a fix for cinnamon-session (and -common) in our fixes unstable repo.
For those of us, who love to live on the edge and have upgraded to cinnamon 2.4 in debian experimental, there is also a fix in our fixes experimental repo.
Thanks, agaida!
greetings
musca
P.S. A fine example for community life!
Issue marked as fixed.