old plasma windows fade occasionally after opening new windows

[Yatian Liu]

I recently upgraded to Kubuntu 19.04 with KDE Plasma 5.15.4 and Qt version 5.12.2 from Kubuntu 18.10 using the system upgrade app. After upgrading, when I open new windows, the old windows will occasionally fade. Moreover, the pop-up menus (for example, the "Other bookmarks" menu in Chromium) may also fade. The screenshots of faded windows and menus are shown in the attachments. The old Kubuntu 18.10 does not have this problem.

When I hover my mouse over any icon of an opened app in my icon-only task manager for some time and then move my mouse away, the fading effect disappears. Also, the fading effect when opening new windows seems to be similar to the effect when I hover my mouse on icons in my icon-only task manager. I guess this bug may be related to the preview feature of the task manager.

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: plasma-workspace 4:5.15.4-0ubuntu1
ProcVersionSignature: Ubuntu 5.0.0-13.14-generic 5.0.6
Uname: Linux 5.0.0-13-generic x86_64
ApportVersion: 2.20.10-0ubuntu27
Architecture: amd64
CurrentDesktop: KDE
Date: Mon May 6 10:03:20 2019
ExecutablePath: /usr/bin/plasmashell
InstallationDate: Installed on 2018-12-25 (131 days ago)
InstallationMedia: Kubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.2)
SourcePackage: plasma-workspace
UpgradeStatus: Upgraded to disco on 2019-04-19 (16 days ago)

[Scarlett Gately Moore (scarlettmoore)]

This bug is very old, if this is still an issue please update the bug with info from a supported release.