Comment # 1 on bug 1096374 from Stefan Seyfried

Hi Wolfgang,

I have no such problems with nm-applet, blueman and xfce4-power-manager's
systray icons, they always appear fine (note that the xfce4-power-manager icon
needs to be enabled explicitly in xfce4-power-manager-settings under
"Appearance" => "System Tray Icon", the default black/white battery icon with
percentage and time is the xfce4-power-manager panel plugin, which is a
different thing than the systray icon. For convenience I have enabled both)

One thing to test the race-condition theory would be: issue "xfce4-panel
--restart" from the Alt-F2 command line. This restarts the panel. If the icons
appear then, but not at login, this could hint the developers where to look.

... which brings us to the people who can fix your issue (I probably can't ;-):

https://bugzilla.xfce.org/ 

The guys over there are friendly, the time to resolve issues ... depends. If
you file a bug there, please mention the bug number here, so that I can track
that bug for progress, and maybe answer questions about our packaging etc.

Maybe this bug is related to bug#1074214, which I unfortunately also cannot
reproduce :-(