When you click on Samba Server in Yast2 you get a prompt to install additional
packages. After those packages are downloaded they are installed one by one.
In previous versions of openSUSE that little window which shows installation
progress is permanent for all packages and after that closes. The problem is
cosmetic but now for every package the window is closed and reopened which
causes the background window of Yast to flicker from black & white to regular.
This is caused by default KDE desktop effects.
The solution would be to make install progres one window for all packages which
will not cause the flicker. Evidently this is only reproducible in KDE.