I don't know if have this on your computers but the mouse seems to use lot of ressource in the graphic display. If I set the Earth to spin continuously, I get ...

More than 10 frames/s if mouse is outside the window,
around 3 frames/s if mouse is over the title bar,
and around 1 frame/s if mouse is over the graphic zone.

I agree, this results may vary depending on computers & video cards but it seems strange that difference between mouse over & mouse outside the graphic window is greater than 10 times.

Were do you read the fps?

> Were do you read the fps?

It's just an estimate. If your box isn't too fast, you can use a watch for cases below than 5 fps. I've first seen this problem (if any) just by moving mouse outside the graphic window.