I'm not sure if it's related to the test patches only but this is a FPS strange behaviour report:
In windowed mode, by using Shift+F4:
Screenshot 1: The window has the focus, normal FPS.
Screenshot 2: The window does not have the focus (clicked on the desktop), normal FPS.
Screenshot 3: The window does not have the focus, but the FPS are stuck to 64.
Screenshot 3 is showing the most usual behaviour I got when the windows does not have the focus. FPS are stuck to 64.
I haven't found a way (yet) to reproduce every time the normal FPS I got in screenshot 2 (no focus, normal FPS).
Now something even more strange when there are no cars on track:
Aucune voiture en course = No cars on track
Screenshot 4: FPS suddenly drop down to about 40 FPS (focused)
Screenshot 5: 32 FPS only if the window doesn't have the focus (Hm that's half the 64 FPS we have seen before)
Screenshot 6: Everything is normal when there are cars on track (focused)
Screenshot 7: Same view with no cars on track (focused)
Screenshot 8: Same behaviour on another track and in full screen mode
Windows XP, DirectX 9.0c (March 2008), Radeon HD 3870.
Catalyst 8.2 video driver only with ATI Tray Tools (Control Center is not installed).
Vsync is OFF in both video driver and LFS. AA is OFF, AF 4x (set in-game, video driver is set to application preference).