Created attachment 150367 [details]
Spawning several instances of LO Writer (unpinned, then pinned, then pinned & repositioned on the panel)

SUMMARY
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When grouping, the Icon-Only Task Manager indicates multiple opened windows with a little green "+" icon over an application's task bar icon. This behavior, however, is broken on LibreOffice applications (e.g. Writer) that are PINNED DOWN AND THEN MOVED across the task bar.
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STEPS TO REPRODUCE
1. If pinned, close and unpin any LibreOffice application from the Icons-Only Task Manager.
2. Open Writer, for example, and then open another instance of it.
3. The Icons-Only Task Manager will now indicate that several windows of the application are open by displaying a green "+" on the bottom of the application's icon.
4. Pin the LO app, e.g. Writer, to the task bar and then MOVE IT TO ANOTHER POSITION.
5. Close all windows of the application, then then re-open several instances.

OBSERVED RESULT
When I've pinned a LibreOffice application to the Icons-Only Task Manager and keep the icon in its default position on the panel, it displays several open windows with a "+" sign over its icon, as it should. However, once I've MOVED the pinned icon to another position on the panel, no more "+" sign appears.

EXPECTED RESULT
The "+" indicator should reliably appear each and every time a pinned (grouped) LibreOffice application has several windows opened and its icon has been moved to different positions on the panel.

OS: KDE neon 5.25
KDE Plasma Version: 5.25.2
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.5
Graphics Platform: X11


ADDITIONAL INFORMATION
- This might be an upstream issue with LibreOffice, as I've observed that LO also behaves incorrectly in regards to window management on the Budgie desktop or the Mutter window manager respectively.

- LibreOffice Version: 7.2.7.2 / installed from LibreOffice's official "still" PPA / UI render: default; VCL: kf5 (cairo+xcb)