After upgrade yesterday to Tumbleweed from 13.2 (which worked fine)
Heavy flicker/tearing of whole KDE desktop, particularly when displaying
overlay windows (eg logout countdown)
Switching off compositing cures the problem, but I can find no combination of
settings that allows compositing to be on without a problem.

Intel i5-4670K using inbuilt graphics. 
glxgears works fine/glxinfo looks fine.
Nothing on Xorg.0.log, nothing in journalctl, and only an (apparently)
unhelpful 
"No such method 'compositingNotPossibleReason' in interface 'org.kde.KWin' at
object path '/KWin' (signature '')" 
in the Desktop Effects - System Settings window after re-enabling OpenGL
detection.