Comment # 1 on bug 1105229 from Marek Pa��nikowski

I disabled the offending repository and reverted all the packages to the ones
provided by default and got the proper rendering back.

# journalctl | grep plasma
[ log entries identical to the previous configuration ]
Aug 18 09:52:24 obikawa14 ksmserver[2016]: org.kde.kf5.ksmserver: Starting
autostart service  "/etc/xdg/autostart/org.kde.plasmashell.desktop"
("/usr/bin/plasmashell")
Aug 18 09:52:25 obikawa14 plasmashell[2031]: org.kde.plasmaquick: Applet
preload policy set to 1
Aug 18 09:52:25 obikawa14 plasmashell[2031]: Using Wayland-EGL

The only difference from before is the lack of the last line complaining about
the EGL implementation. Which suggests that the upcoming "Wayland-EGL" is
broken.