Ok, this turned out to be a lot of issues:
From 2.6.31 and onwards the kernel chooses as default 848x480 when at least the ddx by default chooses 1024x768 (and so did the kernel before, but that could have been because of a non-existent but enabled LVDS).
and for the "xrandr --output TV1 --set mode PAL && xrandr --output TV1 --mode 1024x768" breaks glx-apps:
The git tag v2.6.31 works from linus kernel tree as well as in the stable tree provided by gregkh. But between v126.96.36.199 and .2 there is breakage introduced in the stable tree, but reverting that on top of v188.8.131.52 still fails so I guess there is more then one breaking commit here. So v184.108.40.206 is fine but not the later in the stable series.
Linus kerneltree broke between 2.6.32-rc3 and 2.6.32-rc4 with the following commit:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=0d0884cee3099ec1271a5d379c39b66de1e31923 (drm/i915: Multiply the refresh by 1000 in TV mode validatiion)
and reverting that commit on top of current tree makes my glx-related problems go away (i.e. the picture stops flicker vertically over the screen).
So which one should we track here and which one should I open new bugs for?