This bug affects all LO 6.x apps. It was not present in 5.x.
When you launch (for example) LO Writer, it creates a generic window with the class WM_CLASS "libreoffice LibreOffice 6.0". After a moment, it changes the WM_CLASS to "libreoffice libreoffice-writer". This causes issues in KDE Plasma: https://bugs.kde.org/show_bug.cgi?id=396871
Steps to Reproduce:
1. Use KDE Plasma (any recent version)
2. Use an Icons-only task manager
3. Install LibreOffice 6.x
4. Pin LO Writer to your Icons-Only Task Manager and move it so it's not the last pinned icon
5. Click on the LO Writer icon that you've pinned to your Icons-Only Task Manager
Because the WM_CLASS value changes, a new icon is created at the end of the list rather than the Task Manager knowing that it's an instance of the pinned app and re-using the pinned app icon. See the video in https://bugs.kde.org/show_bug.cgi?id=396871 (https://drive.google.com/file/d/1_G69tnyXNT_CQPBC8JOCl3LIgL7zyxyB/view?usp=sharing)
The WM_CLASS value should not change, which would allow the Task Manager to know that the spawned window is an instance of the pinned app.
User Profile Reset: Yes
The issue could be resolved by having each LO app use the same WM_CLASS value for the generic window as for the actual UI window that the user will interact with.
(it would also be solved by doing away with the whole immediately-spwan-a-generic-dummy-window thing entirely but I imagine that's more architecturally complex or else it would have already been done).
With gtk3 under wayland we don't change the WM_CLASS (or equivalent) which gives rise to the issues of bug 100158. See vcl/unx/gtk3/gtk3gtkframe.cxx with the
// rhbz#1334915, gnome#779143, tdf#100158 comment
so it is possible to survive without changing the WM_CLASS
that said we've changed the WM_CLASS for years and years, so "This bug affects all LO 6.x apps. It was not present in 5.x." sounds odd to me wrt the WM_CLASS hackery