I have made a small test-case for your convenience: http://tvz.myhomework.nl/ckeditor_problem.html
The simple container has opacity (CSS3) set. When you click the Maximize button, the entire container disappears, leaving only the background left.
When I remove the opacity from the container, the Maximize button works fine.
CKEditor is version 3.5.3. I am using Firefox 4.01. Internet Explorer 9.0 seem to work okay.
'Maximize' makes website disappear with Opacity (FF4)