LubuntuNext 17.10 - When not run from terminal, fails upon "Install"

I recently installed Lubuntu Next 17.10.

I have been using Flashpeak-SlimJet as a browser, but it is not in the repositories,
so I download the .deb file and use gdebi to install it.

The version of gdebi that Lubuntu Next installs is gdebi-kde, presumably because LN uses Qt.

However, as described at:
https://bugs.launchpad.net/ubuntu/+source/gdebi/+bug/1731803
gdebi-kde is not usable, and since I needed to install a .deb,
I installed the gtk version, gebi.

That seems to work, until one clicks on "Install", whereupon the window disappears
with no message, never to return...

When run from terminal, the window disappears, but another appears.
This one asks for my password, and when provided one, runs to completion, installing the package.
(I did run it without terminal, and looked amongst my other desktops, thinking that perhaps the
password window was there, but displayed in the wrong desktop, but found nothing.)

It is possible that adding "sudo " to the .desktop file "Exec" would solve the standalone menu invocation, but I am not sure that would help when using the right-click context menu from the desired .deb (and if not, how one would fix that (surely more common) situation).

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scott@scott-Asus-M2N68-AM-PLUS:~$ uname -a
Linux scott-Asus-M2N68-AM-PLUS 4.13.0-17-generic #20-Ubuntu SMP Mon Nov 6 10:04:08 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
scott@scott-Asus-M2N68-AM-PLUS:~$ lsb_release -dsc
Ubuntu 17.10
artful
scott@scott-Asus-M2N68-AM-PLUS:~$ echo $DESKTOP_SESSION
QLubuntu

scott@scott-Asus-M2N68-AM-PLUS:~$ apt-cache policy gdebi
gdebi:
  Installed: 0.9.5.7+nmu1ubuntu3
  Candidate: 0.9.5.7+nmu1ubuntu3
  Version table:
 *** 0.9.5.7+nmu1ubuntu3 500
        500 http://us.archive.ubuntu.com/ubuntu artful/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu artful/universe i386 Packages
        100 /var/lib/dpkg/status
--------------------------------------------------------------------

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: gdebi 0.9.5.7+nmu1ubuntu3
ProcVersionSignature: Ubuntu 4.13.0-17.20-generic 4.13.8
Uname: Linux 4.13.0-17-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.20.7-0ubuntu3.5
Architecture: amd64
CurrentDesktop: LXQt
Date: Sat Nov 25 14:34:46 2017
InstallationDate: Installed on 2017-11-06 (19 days ago)
InstallationMedia: Lubuntu-Next 17.10 "Artful Aardvark" - Beta amd64 (20171014)
PackageArchitecture: all
SourcePackage: gdebi
UpgradeStatus: No upgrade log present (probably fresh install)