This demo is showing that IE7B2 is now supporting left and right properties together but that it still hasn't got the bottom co-ordinate (and therefore the height) to calculate properly yet?
In the CSS there is a conditional block where if you change the target to IE7 it will show the desired results. In order to get a bottom value, I had to sum all of the elements ascending containing blocks, top and bottom co-ordinates and then add the required value - ??