Comment # 7 on bug 1123131 from Cor Blom

Also tried it out. With a global menu the kde5 version is better than the gtk3
one, because with gkt3(-kde5) there are two menubars next to one another. This
is not the case with the kde5 vcl.

I have another problem with the kde5 plugin: it seems the windowclass is not
set correctly. This causes problems with the icons only taskbar and programs
grouping. When I start writer and after calc, they are grouped as if the same
program. for both the window class is soffice.bin..

Probably something to do with

https://bugs.documentfoundation.org/show_bug.cgi?id=119202

The kde bug referred to in that bug provided a work around, but that does not
work anymore apparently.