Overscan correction only works in native resolution

I am using the component TV-out on my GeForce 9400. I set TVStandard to HD1080i.
This mode works fine for watching TV and games that can scale to this resolution,
and overscan compensation even works that I set up in my xorg.conf.

The problem is that when the mode needs to be switched, I get the overscan problem.
If I set metamode parameters to deal with this for the desired mode, the GPU/driver
fails to either change the resolution OR apply the overscan compensation settings,
drawing the whole frame in just the upper-left corner of the 1920*1080 screen.