Bug#942676: mate-menu: Can't add MATE Advanced Menu to panel

[Mike Kupfer <mkupfer@alum.berkeley.edu>]

Package: mate-menu
Version: 19.10.2-1
Severity: important

Dear Maintainer,

I had an instance of the MATE Advanced menu in my panel.  After an
upgrade a couple weeks back (sorry, I don't remember exactly when),
that spot in the panel was blank, and clicking in that area had no
effect.

Since then I have reset my panels (right-click on a panel, select
Reset Panel) and tried to re-add the advanced menu.  I select the
advanced menu and click on "Add", but I don't see anything happen.  No
lines are added to .xsession-errors.

I have tried hiding $HOME/.config and logging out/in; that doesn't
help.

Turning compositing on/off doesn't help.

The system is a VirtualBox VM.  I've seen the problem with VirtualBox
6.0.12 and 6.0.14 on the host.  I tried changing the video adapter
from VBoxVGA (no-3D acceleration) to VMSVGA (with 3D acceleration);
didn't help.  VBoxSVGA (with 3D acceleration) doesn't work, either.
Updating to the 6.0.14 VirtualBox Guest Additions did not help.

I'm able to add other applets to the panel (e.g., System Monitor,
Window Selector).

-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 5.2.0-3-amd64 (SMP w/2 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages mate-menu depends on:
ii  dconf-gsettings-backend [gsettings-backend]  0.34.0-1
ii  gir1.2-gtk-3.0                               3.24.12-1
ii  gir1.2-matedesktop-2.0                       1.22.2-1
ii  gir1.2-matemenu-2.0                          1.22.1-1
ii  gir1.2-matepanelapplet-4.0                   1.22.2-1
ii  libglib2.0-bin                               2.62.1-1
ii  mozo                                         1.22.2-1
ii  python3                                      3.7.5-1
ii  python3-configobj                            5.0.6-3
ii  python3-pkg-resources                        41.2.0-1
ii  python3-setproctitle                         1.1.10-1+b2
ii  python3-unidecode                            1.1.1-2
ii  python3-xdg                                  0.25-5
ii  python3-xlib                                 0.23-2
ii  xdg-utils                                    1.1.3-1

mate-menu recommends no packages.

Versions of packages mate-menu suggests:
pn  software-center  <none>
ii  synaptic         0.84.6+b1

-- no debconf information