Tearing when using PresentPixmap

PresentPixmap is a method in the Xorg Present extension that provides the ability to update the content of a window during vblank. pixmap submitted via PresentPixmap should be queued for update during the specified vblank period to avoid tearing.

However, when using the NVIDIA driver, PresentPixmap still causes tearing.

Is this a problem in the NVIDIA driver?

And using PresentPixmap with NVIDIA seems to cause high CPU usage in the Xorg process.