Flash :: AS3 - Manually Created MovieClips And 'Convert Into Compiled Clip'

I want to use compiled clips to speed up compilation. But I've found following problem: I've got Foo class, which extends MovieClip and is set as 'Class' to one of library's symbol (this symbol is also called Foo). This symbol (Foo) has a MovieClip child, whose instance name is FOO_CHILD. I'm referencing this child inside Foo class constructor like this:

public function Foo(){
childReferennce = this.getChildByName("FOO_CHILD");
}

Now, when I use 'Convert into compiled clip' option on Foo library symbol it complies fine. But when I try to use it on stage, then I've got runtime error (ReferenceError: Error #1056 which says that it is not able to create "FOO_CHILD" property on my Foo class).