Also, I have installed xfce but "top" shows that it is running gnome-session. Wtf?
Don't wonder, the aim of Xfce is not to recreate the wheels but to make the best out of it: this mean, Xfce uses both KDE and Gnome libraries, aside from the regular Gnu packaged libraries. Within Xfce you are given the options to run either or both Kde or Gnome services. An Xfce session is a session that always runs libraries from either or both Kde or Gnome.
It appears that your installation of Xfce has some problem. Try reinstall it again and have installed all needed Kde and Gnome libraries.