This is a Zone bug.
I've noticed that.
It happens when you type below the text window and then hit "HTML preview" and then go back to "message" Text".
Yeah, posting from the Preview works and I found you can maximize the reply window or- grab and drag the lower right hand corner to get to the post button.
Every once in awhile, I get kicked of the Nexus- haven't figured that out yet.
F11? C'mon Tom, get off your wallet and by a modern keyboard. With IE8, Not only do the toolbars and address bar disappear, you don't see the task bar either. It's 'true' full screen.