AutoCAD .NET :: Selecting Nested Entities And Inheriting From BlockReference

My primary goal in this exercise is to select a nested polyline within a block and have access to its grips. I'm still not even sure if it's possible.

However, before I'm even getting to that stage I'm hitting some problems. I have some custom objects which all in some way or another inherit from BlockReference:

BlockReference

-Derived Abstract Class with common attributes

-Derived Concrete Class1

-Derived Concrete Class2

-Derived Concrete Class3

I insert instances of my derived concrete classes using jigs( Class2 for example is created using a polyline jig). However, when I select the block generated from it using a PromptSelectionResult, it returns a BlockReference, not the derived concrete class, not the derived abstract class.

When I try and cast that as the correct class type I get an error telling me I can't cast from the Base class to any of the derived classes.

So, firstly, why is it returning a BlockReference when the object I'm clicking on is an instance of a type that indirectly inherits BlockReference? And is it even possible to gain access to a nested entity's grips? I followed post here: [URL] .... but it doesn't give me what I need.

I've tried ed.GetNestedEntity and the AllowSubSelections property of PromptSelectionOptions and had little joy.