Hello everybody,
as I wrote I was investigating in sync problems I experienced.
I haven't tested it thoroughly, but on a first glance it looks like adding the kernel parameter "elevator=cfq" to grub's menu.lst to run another scheduler solves the problem (this was suggested on vdr-portal.de). Thus
kernel /boot/vmlinuz-2.6.12-1-386 root=/dev/hda1 ro vga=0x31A elevator=cfq
did it for me.
Thought to just let you know, in case someone else is experiencing similar problems.
HTH, André