Since that reported issue, i've made three fresh installations: utopic 32, utopic 64, trusty 32
they all run gnome-shell.
As a result, the error reported here has not been seen on these installations: one use its own 'home' folder, the 2 others share a /home partition (the same one used when that report has been opened).
So it seems that some config paramaters/symlinks or package/folder rights (on the system itself, not those inside /home) are wrong or left behind after upgrading.
Feedback
Since that reported issue, i've made three fresh installations: utopic 32, utopic 64, trusty 32
they all run gnome-shell.
As a result, the error reported here has not been seen on these installations: one use its own 'home' folder, the 2 others share a /home partition (the same one used when that report has been opened).
So it seems that some config paramaters/symlinks or package/folder rights (on the system itself, not those inside /home) are wrong or left behind after upgrading.