I don't know whether it is possible to get rid of Evolution, I think it is required by some ubuntu-desktop meta-package.
Anyhow, I do think this has to do with Xfce. Before Gutsy, I used Xfce4 as my desktop (on ubuntu, not xubuntu though), now I switched back to GNOME and along with that, some day, that bug occured.
I don't know whether it is possible to get rid of Evolution, I think it is required by some ubuntu-desktop meta-package.
Anyhow, I do think this has to do with Xfce. Before Gutsy, I used Xfce4 as my desktop (on ubuntu, not xubuntu though), now I switched back to GNOME and along with that, some day, that bug occured.