Hi, there :
I encountered an odd situation and it is only happens on IE. Our project is a Flash 3D Game using Stage3D, and the Game's GUIs are created by CS6. When our game switch from the full screen( StageDisplayState.FULL_SCREEN_INTERACTIVE or StageDisplayState.FULL_SCREEN ) to normal screen ( StageDisplayState.NORMAL ), the performance of the Game GUIs decline to approximate a half FPS of full screen mode. But this condition is only happens on IE.
The Game is normal screen when it is initialized and the performance is as same as fullscreen. The performance degradation only happens after switching to normal screen mode from full screen mode.
p.s. : When the mouse is out of the view, the performance become better, from 20 fps up to 50 fps. But is still not as same as the original 60 fps.
p.s. 2 : My colleague told me the Flash Pro CS6 be used to built a single swc file per GUI, and then package all ui swc files to one swc file by Flex Framework SDK( the command is "compc" ). and the IE version = 9.0.8112.16421, the Flash Player Version = 11.6.602.155.
p.s. 3 : I have utilized Adobe Profiler Scout to observe the application, and I found that when it switches to normal screen mode from full screen mode, the time 「Waiting for GPU」 in 「Inactive」 grows up from 10ms to approximate 30ms which is triple. And in the 「Activity Sequence 」tab, it shows that the 「Waiting for GPU」 happens in the 「Copying to screen 」in 「DisplayObject List」.
This does sound like a specific bug with IE. It would be great if you could file a bug report here (https://bugbase.adobe.com/), so we can get somebody to look into it.
btw, Flex is really not a good framework for games - it's really slow and heavyweight. If you're just wanting some lightweight UI elements, you might want to check out the Feathers framework, which is built on top of Starling: http://feathersui.com/