To reproduce you need a dual monitor system.
The first monitors resolution should be less than the second one. In my case my main monitor (The one that has the start bar) is set to run at 1024x768. My second monitor is set to run at 1600x1200. When I move IDEA into the second monitor and press maximize button it only goes up to 1024x768 which is the resolution of the first monitor.
In addition when I make edits in a file there used to be an indicator in the tab for that file like a * that said that file is modified. I don't see that in IDEA 5.0.
IDEA 5.0 RC3 #3424
Windows XP Professional