Can't restart/shutdown from the panel icons, logged out instead

[Daniel González Gasull]

Hi.

About a week ago the icons for restart and shutdown in the panel
stopped working properly and when I click on them I still get the
popup window "Are you sure you want to restart?  Restarting in 30
seconds".  But when the time goes out, or if I click on the OK button,
I get logged out of my Xfce session instead, into the LightDM screen.
Strangely suspend works fine.

Someone on the #xfce IRC channel suggested it could be a problem with
polkit, but I haven't found anything in my research.

I log into my session automatically, since I have autologin-user and
autologin-user-timeout set in my /etc/lightdm/lightdm.conf.  But
unsetting them didn't have any effect.

I am using Debian Testing.

How can I fix this?

Does anybody know at least how to see logs of exactly what happens
when I click on the restart or shutdown buttons?

Thank you in advance.

-- 
Daniel González Gasull