That's utterly new to me... There's not a lot of difference while the screensaver is active. It simply turns off the screen, everything else remains the same (well, and every 5 seconds the screen is re-deactivated in case it's been turned on with the power button, but that shouldn't cause any troubles...).
Maybe your device switches to a lower CPU rate when the screen's off. In this case, there's nothing I can do about it. You could try to work around it with higher buffer or priority.
Maybe the new beta (download area on
www.sto-helit.de) helps a bit, too. There are some minor tuning / thread priority changes in it...