I'm trying to get my head around an interop issue. I have a legacy COM
DLL that I've wrapped using TLBIMP. This DLL exposes a standard
CoClass (let's call it Widget), and in the resulting interop assembly
I see the following

 .class public auto ansi import WidgetClass
        extends [mscorlib]System.Object
        implements IWidget,
                   Widget
 {
 } // end of class WidgetClass

 .class interface public abstract auto ansi import Widget
        implements IWidget
 {
 } // end of class Widget

 .class interface public abstract auto ansi import IWidget
 {
 } // end of class IWidget

OK, this makes sense -- I get a managed type to represent the CoClass
itself (WidgetClass), which I can instantiate. I also get a managed
interface to represent the COM interface (IWidget), which obviously I
can't instantiate, because it's an interface.

My questions are:

1. What's the Widget interface for? And why on earth am I allowed to
instantiate it? Why isn't the compiler throwing this instantiation out
like it does for IWidget? I don't see any difference between these two
interfaces -- how does the compiler know to give Widget special
treatment to break the rules of Object Orientated Programming?

2. The COM DLL exposes another CoClass (Thing) which has a property of
type Widget:

.method public hidebysig newslot specialname abstract virtual
       instance class Widget
       marshal( interface)
       get_Widget() runtime managed internalcall
{
 .custom instance void
[mscorlib]System.Runtime.InteropServices.DispIdAttribute::.ctor(int32)
= ( 01 00 0C 00 00 00 00 00 )
} // end of method IThing::get_Widget

However, from .NET if I try to do this:

Thing aThing;
... get aThing from somewhere ...
if (aThing != null) {
 string s = aThing.Widget.WidgetStringProperty;
}

I get (randomly, it seems) either a COMException or a
NullReferenceException at the point of assignment.

The only way I can access WidgetStringProperty is to do this:

string s = ((WidgetClass) aThing.Widget).WidgetStringProperty;

or

WidgetClass wc = (WidgetClass) aThing.Widget;
string s = wc.WidgetStringProperty;

either of which is most inconvenient.

What am I missing here?