Starting yast modules in GUI (Qt) version in a Plasma workspace, either by
executing
    xdg-su -c "/sbin/yast2 some_module"
as defined in the desktop files or by selecting a module in the control center,
the module window is shown with the generic X.org window, and in the task
manager panel shown just with "YaST2" name (so without any module name) and
grouped by "ruby" name.

xprop reports e.g.

_NET_WM_ICON_NAME(UTF8_STRING) = 
_NET_WM_NAME(UTF8_STRING) = "YaST2"
WM_NAME(STRING) = "YaST2"
WM_CLASS(STRING) = "ruby", "YaST2 - sw_single @ klux.site"

which explains why Plasma uses that info.

Interestingly when starting
    /usr/lib/YaST2/bin/y2base sw_single qt
directly, the properties are

_NET_WM_ICON_NAME(UTF8_STRING) = 
_NET_WM_NAME(UTF8_STRING) = "YaST2"
WM_NAME(STRING) = "YaST2"
WM_CLASS(STRING) = "YaST2", "YaST2"

Though still not resulting in the proper window name and title (e.g. matching
what the icon and name in the module desktop file).

More interestingly, when doing the latter as normal user, so that the
non-root-continue dialog pops up, the window at that state has 

_NET_WM_ICON_NAME(UTF8_STRING) = 
_NET_WM_NAME(UTF8_STRING) = "YaST2 - Software Management"
WM_NAME(STRING) = "YaST2 - Software Management"
WM_CLASS(STRING) = "YaST2", "YaST2"

so it seems something overrides the proper window title (*WM_NAME) with a plain
"YaST2" while completing the init.

Some links to related documentation:
https://tronche.com/gui/x/icccm/sec-4.html#WM_CLASS + ctrl+f for WM_CLASS on
https://wiki.gnome.org/Projects/GnomeShell/ApplicationBased

Expected behaviour:
Windows for Yast modules have same name and icon in Plasma (windows and
taskbar) as specified in the respective desktop files (e.g.
/usr/share/applications/YaST2/sw_single.desktop)