SUMMARY

Windows of some programs cannot be properly restored by clicking on their icons on the task switcher widget (regardless of which of the several alternative task switcher widgets is used). After certain specific sequences of operations the window will go into a state where clicking its taskbar icon will cause the window to alternately minimize and maximize UNDERNEATH another window which is currently on top. If the "occluding" window is not maximized itself, it can be clearly seen that the problematic window does minimize/restore and does become active when restored, it just doesn't go to the top.

STEPS TO REPRODUCE
1. Open Firefox and unmaximize its window
2. Open PHPStorm, maximize its window and make sure it is on top and active
3. Minimize PHPStorm window by clicking on its taskbar button/icon
4. Try bringing the PHPStorm window back by clicking on its taskbar button/icon again


OBSERVED RESULT

PHPStorm maximizes and becomes active, but does not move to the top. The unmaximized Firefox window remains on top.

EXPECTED RESULT

PHPStorm window should move to the top in addition to being restored and becoming active.


SOFTWARE VERSIONS
(available in About System)
KDE Plasma Version: 5.13.90 but noticed in stable too
KDE Frameworks Version: 5.50.0
Qt Version: 5.11.2

ADDITIONAL INFORMATION

I have verified that no specific window rules are in effect, and I have restored all window manager defaults.

I am not sure if it is not a PHPStorm bug. I will report it to Jetbrains too.