Comment 21 for bug 1267977

Random guess:
1. ensure that triple buffering is really enabled:
  grep -i triple /var/log/Xorg.0.log
2. next convince kwin about it
   export KWIN_TRIPLE_BUFFER=1
   kwin --replace &

The problem here is that full scene repaints do not seem to cause a problem, so it cannot be swapping by itself (though you should ensure that flipping is enabled in nvidia-settings, GL settings page) and either frontbuffer reading or buffer_age.

What's even more weird is that you claim tearing for frontbuffer reading, what can only have two pot. causes:
1. no flipping (see above)
2. tearing in the client (activate the "show paint" effect, it's worthless for buffer_age or full scene repaints, though)

But either case would also apply to full scene repaints.

One last resort: try to disable blurring.