missing entries in whisker menue, because of missing "DesktopNames=XFCE" in xubuntu.desktop

Installing xubuntu 16.04 and LTSP I realized missing entries in whisker menue when logged into a ThinClient. Logged in directly to the server they appeared.

The missing entries are .desktop-files stored in /usr/share/applications
with an entry
"OnlyShowIn=XFCE;"
commenting this entry in an .desktop-file
"#OnlyShowIn=XFCE;"
the entry appeares immediately.

env | grep XDG
reveals
XDG_CURRENT_DESKTOP=Xubuntu Session

the invironment isn't set correctly. It should be
XDG_CURRENT_DESKTOP=XFCE

This is done by
/opt/ltsp/i386/usr/share/ldm/rc.d/X50-generate-env
"greping" the files in
/usr/share/xsessions

In
xubuntu.desktop
should be an entry:
DesktopNames=XFCE

Then the entries appear.

dpkg -S xubuntu.desktop
xubuntu-default-settings: /usr/share/xsessions/xubuntu.desktop

There are similar bugs for lightdm/mate:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=809803
https://bugs.launchpad.net/lightdm/+bug/1383321

The missing entries are:
Settings (Einstellungen):
Display (Anzeige)
Workspaces (Arbeitsflächen)
Accessibility (Barrierefreiheit)
Notifications (Benachrichtigungen)
Preferred Applications (Bevorzugte Anwendungen)
Bluetooth Adapters (Bluetoothadapter)
Orage preferences (Einstellungen für Orage)
Settings Editor (Einstellungsbearbeitung)
Appearance (Erscheinungsbild)
Window Manager Tweaks (Feineinstellungen der Fensterverwaltung)
Window Manager(Fensterverwaltung)
Panel (Leiste)
Mouse and Touchpad (Maus und Touchpad)
Desktop (Schreibtisch)
Session and Startup (Sitzung und Startverhalten)
Xfce Panel Switch (Xfce-Leistenschalter)

Accessories (Zubehör):
File Manager (Dateiverwaltung)
Notes (Notizen)
Terminal Emulator (Terminal)

Thanks!

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xubuntu-default-settings 16.04.6 [modified: usr/share/xsessions/xubuntu.desktop]
ProcVersionSignature: Ubuntu 4.4.0-22.39-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Tue Jun 7 18:59:02 2016
InstallationDate: Installed on 2016-04-26 (42 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: xubuntu-default-settings
UpgradeStatus: No upgrade log present (probably fresh install)