CheckBox dynamic initiation error

Steps to reproduce:
1. Create a class extending the mx.controls.CheckBox control, e.g. myCheckBox.
2. Compile the class into a swf file using Adobe Flex 3 SDK.
3. Load the swf file into your application using a loader, then after the load complete use flash.utils.getQualifiedClassName(loader.content) to get the class name.
4. use loader.contentLoaderInfo.applicationDomain.getDefinition(className) to get the object class, then create an instance of that class (myCheckBox), then add it to the application.

Actual Results:
A Button control appears instead instead of a CheckBox control.

Expected Results:
A CheckBox control should appear.

Workaround (if any):