Changes from RC1 to RC2/RC3

Hello, I use a custom css for the editor area. In RC1 when I added body-width to the CSS, the inner editor area changed based on the width I set.

In RC2/RC3 the width does not change. The strange thing is all other CSS tags seems to work on the body. Tried changing background color and everything works ok - except when trying to set the width as said.

Is there any "codes" that overrides the inner body-width in the editor in the two last RC's? I find it nice to set the body width since I can set it to something close to what the "production" pages have. And no, changing the Iframe width is not an option