Update Manager, Gtk-CRITICAL, assertion 'GTK_IS_WIDGET (widget)' failed

[Mark Filipak]

There's a bug that shows up in the Update Manager (i.e. mintupdate) log.

From Update Manager (mintUpdate) log (/tmp/mintUpdate/952kecim):
"(synaptic:7604): Gtk-CRITICAL **: 13:31:25.431: gtk_widget_hide: assertion 'GTK_IS_WIDGET (widget)' failed"

What does Gtk say?
'https://docs.gtk.org/glib/func.critical.html' says:
"Logging of a critical error is by definition an indication of a bug somewhere in the current program (or its libraries)."

That is why I'm here -- I'm just trying to be a good citizen. I don't know what the bug's effect is.

Steps to reproduce
Launch Update Manager
Install something ...sorry, I don't remember what the update notification asked me to install.
Look at the log.

Current behavior
Logs a "Gtk-CRITICAL" error

Expected outcome
No error.

Version information
Kernel: 5.4.0-121-generic x86_64
bits: 64
compiler: gcc v: 9.4.0
Desktop: MATE 1.26.0
wm: marco
dm: LightDM
Distro: Linux Mint 20.3 Una
base: Ubuntu 20.04 focal

Thank you, and thank you for Ubuntu.