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).
When there is no car in the race, there is a minimum sleep of 25 ms - same as in entry / game setup screens. So the frame rate won't go above 40 ms in that case. This is because LFS wants to avoid using all your CPU / GPU power when there is nothing going on.
I don't know why you have two different non-focussed frame rates (64 / 205). But it's normal for a program without focus to be given less CPU time by windows.
EDIT : So the only mystery is why your unfocussed frame rate with cars in race sometimes goes down to 64. Maybe you could check the CPU usage in the CTRL+ALT+DELETE menu in this case.
For some strange reason in Y14 I get blocks for cars and blocks for text and buttons often.
And also it crashes like mad!
But Y15 doesn't crash as much and I haven't had the block problem yet.
P... = CPU usage
Screenshot 1: LFS has the focus. CPU usage is about 30% average.
Screenshot 2: LFS doesn't have the focus. I still have normal FPS but CPU usage is about 3-5% lower average.
Screenshot 3: LFS doesn't have the focus. FPS are stuck to 64 and CPU usage is 0.
It seems that I got normal FPS with no focus when I've just started LFS but after using Shift+F4 many times, and/or opening/closing other apps, it got stuck to 64 FPS and won't go back to normal FPS again.
Still I haven't yet found a way to reproduce that every time
Although I noticed the 'loss' of a GDI object in screenshot 2.