[Marshall Plan] When you a ComboBox is in an untrusted child application, it does not open the first time you try. (injection after 11319)

Steps to reproduce:
1. Compile temp_Child2.mxml with -includes=mx.managers.systemClasses.MarshallingSupport.
2. Place temp_Child2.swf on a web server.
3. Update temp2.mxml to point to temp_Child2.swf on your local web server.
4. Compile and run temp2.mxml
5. Try to click on the ComboBox to open it.

Actual Results: The first time you try to open the ComboBox it will open and then immediately close. The second time you open it, it will work correctly.

Expected Results: The ComboBox should remain open.

Workaround (if any):