PrintScreen button unresponsive after trying to take a window screenshot of a notification

[Yu Yang Lin Hou]

Steps to reproduce:
1. trigger a notification pop-up (e.g. ``notify-send Date "`date`"``)
2. mouse over the notification to bring it into focus
3. press `Alt`+`PrintScreen` to attempt to take a screenshot of the window in focus
4. nothing happens and the `PrintScreen` button becomes unresponsive

Nothing is logged and no crash reports are generated. The button simply becomes unresponsive. Restarting Gnome (`Alt`+`F2` and typing `r`restores the functionality of the `PrintScreen` button).

I am running Ubuntu 18.04.5 LTS.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-screenshot 3.25.0-0ubuntu2
ProcVersionSignature: Ubuntu 5.4.0-81.91~18.04.1-generic 5.4.128
Uname: Linux 5.4.0-81-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.24
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Sep 1 20:03:23 2021
DistributionChannelDescriptor:
 # This is the distribution channel descriptor for the OEM CDs
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-bionic-amd64-20180608-47+north-bay-14-15-15p+X56
InstallationDate: Installed on 2020-03-28 (521 days ago)
InstallationMedia: Ubuntu 18.04 "Bionic" - Build amd64 LIVE Binary 20180608-09:38
SourcePackage: gnome-screenshot
UpgradeStatus: No upgrade log present (probably fresh install)