Problems on high performance computer

We have three computers for programming our game and one of then is a high performance (intel E4400@3.0 ; geforce 8800 GTS).
Its running our game at 1500 fps and we have a wierd behavior at those conditions. Characters falls slowly and run faster.
Do you know what is happenig?

Have you tried running the Scene with a fixed scene controller?

how can I do it under NxOgre 0.9 ?