Show element parents - not always working?

[AdamHearn]

Arggh - forgot to fill out subject then back produced a blank form

Could someone please enlighten me on how/why EA decides to *NOT* show inherited elements.

This is the help text from 'Set Parent' (although the dialog is now captioned Type Hierarchy):
Note: Parents that do not have their corresponding related element in the same diagram will display their parentage in the top right corner of the child element, as shown below:

If I reverse engineer a class (C#) that inherits one class and one interface, the diagram shows the class with both parents in the top corners.

If I create a class with the exact same inherited elements, I only see the class.

The difference seems to be that the Type Details (as show in the Type Hierarchy dialog) are not the same. The one that shows has Owned: No and Package <none> where as the class I created has Owned: Yes, Package: 'blah' (I'm assuming this is because I chose the interface from the list of existing model elements). The interface is defined in another package and so going by the help text it should show up (I have the Show Additional Parents option enabled in the diagram).

It's not a huge issue but it would be nice if it worked like the help suggests it does. Perhaps I've not done something correctly?