Dear Maintainer,

   * What led up to the situation?

upgrading my Jessie system

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

I try to login into the system with gdm3, first time I select xfce (the default
one), the second time I try twm as desktop environment

   * What was the outcome of this action?

gnome-shell start and occupy my two CPU. After few minutes I stop gdm3

   * What outcome did you expect instead?

gnome-shell don't have to be started, but I excepted the start of the desktop
environment I have selected

After that I have installed xdm, but with that the gnome3 was started (in few
second) and it work well. But I expected the default xfce to be started.
Then I have installed kdm and finally I successully start the xfce destop
environment.