How to reproduce:

Create an SWC with a class that begins with _ eg:"_MyClass"
Create a new AS3 project and Add to Library the class

If you double click the class you will get nothing.
Also typing the namespace will not give you anything at all.

If the class is inherited by another class that does NOT begin with "_", the new class will have autocomplete but not for the methods it inherits.

This is a little trick used to hide junk classes in SWCs - the test could be a bit less generic though.