Samsung N210, Ubuntu 11.04

I'm not sure if the problem I am having is a bug or just the expected behaviour given the bodge I am using. I have a netbook with a native 1024x600 resolution. Sometimes I need to switch to a higher non-native resolution 1280x750 or 1365x800.

I use a little script that issues the command with all the variables calculated.

Code:
xrandr --fb $H"x"$V --output $device --scale $scale"x"$scale --panning $H"x"$V
This works perfectly in Gnome but fails to work properly in Unity.

In unity issuing the command leaves a black strip across the top and down the right side of the screen that does not get drawn correctly. Only the top panel and the unity launcher are draw in these black areas. A rectangle in the bottom left that would be 1024x600 worth of the 1280x750 does get drawn correctly.

Is it possible that compiz is getting the values for screen geometry from two different sources?

Is this a bug or am I just doing something that shouldn't work? Has anyone had success using zrandr to get higher than native resolution in unity.