Flash Button Component inside of a SWC

I'm publishing a SWC from FlashCC for use in a FlashBuilder Air project and I get errors when I compile.

Inside of the SWC I have a MovieClip with a button component (fl.controls.Button). In Flash Builder I can make an instance of the MovieClip but when I run the app I get a coercion error:

cannot convert flash.display::MovieClip@56ebee1 to fl.controls.Button.

If I remove the button component from the MovieClip and recompile the SWC there's no error.

If i simply try to add a button instance like this:

var b:Button=new Button();

trace(b);

addChild(b);

The button traces but I get this error

[object Button]

TypeError: Error #2007: Parameter child must be non-null