Comment 4 for bug 158421

I experience exactly the same issue with the xserver-xorg-video-intel driver, so it is probably not related to nvidia.

After I rotate the screen with xrandr kde still thinks the screen is WxH instead of HxW. However, I can manually move windows into the area unused by kde. I can also only move my mouse within the HxW area, so X has actually rotated the screen correctly.