- Update -
I have narrowed down the problem somewhat.
I have downloaded the CS6 SDK from here : http://www.adobe.com/devnet/creativesuite.html
and copied exactly the HelloCreativeSuite sample from samples\HelloCreativeSuite included with the SDK. What I have found is that if I use the SWF I have compiled the the panel does not scale properly, but If I overwrite my SWF with the precompiled one included with the sample it works perfectly.
So the problem must be the way the SWF is compiled.
I have added two images below to demonstrate the problem just in case.
The sample SWF works as expected, the content is always at 100% no matter the panel size;
while my SWF seems to ignore the stage.scaleMode property and always resizes to fit the content.
May I ask what exactly that does?
Of course! This reason this argument is necessary stems from the architecture used to load extensions. Each extension is loaded as a sub-application by an application called StageManager. In order for these two swfs to play nicely with one another you have to use something called the Marshall Plan (http://sourceforge.net/adobe/flexsdk/wiki/Marshall%20Plan/ has a pretty detailed overview of the Marshall Plan and why it's necessary).
Another question : Why is there an empty grey strip at the bottom of the SWF when I use csxs:CSExtension in the mxml file?
That's the status bar. You can remove that by setting showStatusBar="false" for your CSExtension.