Comment # 7 on bug 1016612 from Stefan Hundhammer

When I start it as root, I get the Qt file dialogs in both cases, and they have
icons. So it must be something in the user's home directory.

Try this:

  xhost +
  sudo bash
  export DISPLAY=:0
  yast2 -i  

Anyway, this is a bug of the KDE / Plasma 5 desktop, not of YaST.