[pygame] Sync with vertical refresh does not work(?)

[Matthias Treder <matthias4all@xxxxxxxxxxxxxx>]

Hi.

I saw a number of similar posts here and elsewhere on the web, but it
didn't really answer all my questions.
I run an experiment wherein I have to present a number of objects
(each a circle with text on it). At certain poins in time, objects
flash on and off (the circle radius and font size is increased, I wait
5 frames, and then the circle radius is decreased again). I
implemented each object as a Sprite, so I call the update method.
I use fullscreen mode, the objects are relatively large (circle radius
60-70 px) and arranged in a circle spread across large parts of the
screen.

PROBLEM: It seems there is no sync with the vertical screen refresh.
My objects are sometimes torn.

I tried about everything I could conceive of and I am kind of
desparate now. I tried using surface.convert() after I made the Sprite
images, and passing HWSURFACE and/or DOUBLEBUF (I also tried
SWSURFACE) to the set_mode() function. I tried out both
display.update() (passing the corresponding rectangles) and
display.flip(). In the nvidia settings I also enforced vertical sync.
Nothing seems to have any effect.

My questions:

1. Is this a hardware problem or a software problem?
2. In the pygame docs, it says that display.update() is a more
efficient version of display.flip(). However, does display.update()
also wait for screen refresh just as flip() is doing?
3. Is the problem due to the fact that I update large parts of the screen?
4. Is there are any way to get rid of that flickering?

Cheers,
Matthias

PS: I run Windows XP on my laptop @ 3GB RAM and 1,6 Ghz dualcore.
Graphic card is Geforce Go 7600. It's connected to an external TFT
monitor at a resolution of 1280x800@60 Hz.