These are the suttle differences....

Regards, Rolf

Might this help xinomilo?
..rolfie, Thx again (mate wouldn't use that gnome-type file?)

i also have a problem starting luckybackup as root, from menu (runs ok from terminal), but i think it has something to do with Qt in that case, different issue probably..

Sorry, there are some things different on xfce compared to Mate.
Good luck, Rolf

Yep ~ your right. I just figured Xfce being the default - ah, forget the rant.
We did what we could for today, I'll leave this install alone for now, I sent info
to the ML and might just reportbug.
I'll install on other laptop partition, and look for anything different.

Thx again!
asta~

Good luck, Rolf

apt list --installed gparted
Listing... Done
gparted/testing,now 0.32.0-2 amd64 [installed]

If I get more time, I'll check its desktop file also.
I see a reinstall in my future. 
Thx rolfie ~ xinomilo
asta~

#!/bin/sh
pkexec "/usr/sbin/synaptic" "$@"

I recall trying that path entry - with synaptic, but not with bleachbit..

#!/usr/bin/env python
# vim: ts=4:sw=4:expandtab
# BleachBit
# Copyright (C) 2008-2018 Andrew Ziem
# https://www.bleachbit.org
#

"""
Launcher
"""
from __future__ import absolute_import, print_function

import os
import sys

if 'posix' == os.name:
    if os.path.isdir('/usr/share/bleachbit'):
        # This path contains bleachbit/{C,G}LI.py .  This section is
        # unnecessary if installing BleachBit in site-packages.
        sys.path.append('/usr/share/')

if 1 == len(sys.argv):
    import gtk
    try:
        gtk.gdk.Screen().get_display()
    except RuntimeError:
        print("Could not open X display")
        sys.exit(1)
    import bleachbit.GUI
    gui = bleachbit.GUI.GUI()
    gtk.main()
else:
    import bleachbit.CLI
    bleachbit.CLI.process_cmd_line()

I'll install Gparted...see if it reacts same.

There is a shell skript in /usr/bin:

#!/bin/sh
pkexec "/usr/sbin/synaptic" "$@"

The policy looks ok to me. Maybe its worth to check the path settings?

Regards, Rolf

Same versions as in my VM where synaptic works.
Check in /usr/share/polkit-1/actions if you got a file named com.ubuntu.pkexec.synaptic.policy in there.
Rolf

Yes, I do have - for both.
/usr/share/polkit-1/actions/com.ubuntu.pkexec.synaptic.policy
/usr/share/polkit-1/actions/org.bleachbit.policy

English info:

and...

Similar text to an issue fsmithred had dealt with & posted:
https://dev1galaxy.org/viewtopic.php?id=1548
I don't see a quick blink, on my screen.

I'm gonna reboot with the changes and check menu again.
asta ~

apt list --installed synaptic
Listing... Done
synaptic/now 0.84.5 amd64 [installed,local

apt list --installed bleachbit
Listing... Done
bleachbit/now 2.0-3 all [installed,local]

Both /usr/share/applications/ '.desktop' files, just tweaked:

Why my reversed pkexec entry with a dash?

Check in /usr/share/polkit-1/actions if you got a file named com.ubuntu.pkexec.synaptic.policy in there.

Rolf

apt list --installed policykit*
Listing... Done
policykit-1/now 0.105-25+devuan1 amd64 [installed,local]

and..

apt list --installed libpolkit*
Listing... Done
libpolkit-agent-1-0/now 0.105-25+devuan1 amd64 [installed,local]
libpolkit-backend-1-0/now 0.105-25+devuan1 all [installed,local]
libpolkit-backend-elogind-1-0/now 0.105-25+devuan1 amd64 [installed,local]
libpolkit-gobject-1-0/now 0.105-25+devuan1 all [installed,local]
libpolkit-gobject-elogind-1-0/now 0.105-25+devuan1 amd64 [installed,local]

Greetings xinomilo,
Thanks for the "very helpful", show of difference there...a "dash" in mine - none in yours, AND reversed!
Did you use that "rebuilt" mini iso?

mini.iso             07-Feb-2019 12:06          47185920

Same here, thats where I started looking & tweaking also - with no success.

Exec=pkexec bleachbit

I'll remove that dash on both and test.

be right back.. 

Exec=pkexec bleachbit

and it works that way. synaptic also works normally from menu.

apt list --installed policykit*
apt list --installed libpolkit*

Regards, Rolf