Inherited methods not exposed to COM

Question

I have an interface and class that I want to extend. So I created a new interface that inherits the original one. Then I create a new class that inherits the original class and implements the new interface. This way, the extended class should have all the original methods + the extended methods. I works fine in .NET. But when exposing this in a COM DLL the object browser in VB6 clearly shows that only the extended methods are available. The inherited methods are not.

Here is the original interface:

Imports System.Runtime.InteropServices

<ComVisible(True),
    InterfaceType(ComInterfaceType.InterfaceIsDual)>
Public Interface IOriginal

    Function OriginalFunction() As String

End Interface

And the original class:

Imports System.Runtime.InteropServices

<ComVisible(True),
    ClassInterface(ClassInterfaceType.None)>
Public Class Original
    Implements IOriginal

    Public Function OriginalFunction() As String Implements IOriginal.OriginalFunction
        Return "Original result"
    End Function
End Class

And here is the extending interface:

Imports System.Runtime.InteropServices

<ComVisible(True),
    InterfaceType(ComInterfaceType.InterfaceIsDual)>
Public Interface IAlternate
    Inherits IOriginal

    Function AlternateFunction() As String

End Interface

And class:

Imports System.Runtime.InteropServices

<ComVisible(True),
    ClassInterface(ClassInterfaceType.None)>
Public Class Alternate
    Inherits Original
    Implements IAlternate

    Public Function AlternateFunction() As String Implements IAlternate.AlternateFunction
        Return "Alternate result"
    End Function

End Class

How can I make this work like it should? I want VB6 to use the Alternate class with both methods OriginalFunction and AlternateFunction. Right now, only AlternateFunction is showing up as a valid function.

[update] I also tested class Alternate with Implements IOriginal, IAlternate to make sure the compiler would not overlook the IOriginal implementation. But that didn't change anything.