Screencast recording low FPS

I am tying to use screencast (alt f3) to record blender, but for some reason it is only recording about two frames a second, so playback is really fast.

Things I have tried:
Set the framerate on the render tab to 24 fps
In user prefrences - system, set the playback to 24 fps, and wait time to 50ms
Makes no difference if recording PNG’s or direct to AVI jpeg

Any ideas?
Rich