xfce4-session-plugin always save the session during restart/logout.

Actual behavior:
xfce4-session-plugin always save the xfce4 session during logout/restart.

Expected behavior:
xfce4-session-plugin should save the xfce4 session according to value of
SaveOnExit flag from xfce4 settings registry. (key:
xfce4-session/general/SaveOnExit)

Steps to reproduce:
1. Add Session Menu plugin to the xfce panel.
2. Launch some application (e.g. Web Browser)
3. Click on the Session Menu button on the panel and click Log Out.
(Login manager should be appeared)
4. Login to the system
=>
5. Web Browser will be launch.

System Information:
$ cat /etc/issue
Ubuntu 11.04 \n \l

$ uname -a
Linux sly-sub 3.1.0-0301rc2-generic #201108150905 SMP Mon Aug 15 09:12:41 UTC
2011 x86_64 x86_64 x86_64 GNU/Linux

$ apt-cache show xfce4
Package: xfce4
Priority: optional
Section: universe/x11
Installed-Size: 40
Maintainer: Xubuntu Developers <email address hidden>
Original-Maintainer: Debian Xfce Maintainers
<email address hidden>
Architecture: all
Version: 4.8.0~ubuntu1
Depends: xfwm4 (>= 4.8.0), xfconf (>= 4.8.0), xfce4-settings (>= 4.8.0),
xfce4-panel (>= 4.8.0), xfdesktop4 (>= 4.8.0), thunar (>= 1.2.0), thunar-volman
(>= 0.6.0), xfce4
-utils (>= 4.8.0), gtk2-engines-xfce (>= 2.8.0), xfce4-session (>= 4.8.0),
xfce4-appfinder (>= 4.8.0), xfce4-mixer (>= 4.6.1), orage (>= 4.8.0)
Recommends: xorg, desktop-base (>= 5.0.4), tango-icon-theme (>= 0.8.90)
Suggests: xfprint4, xfce4-goodies
Filename: pool/universe/x/xfce4/xfce4_4.8.0~ubuntu1_all.deb