Using implements behind an Excel worksheet function

Since an excel worksheet is represented by a class module in vba, you might be tempted, as I was, to use the implements keywords behind a worksheet.
This would allow you to use polymorphically an Excel worksheet and could open-up differ possibilities.
Howev this is my advice

DO NOT USE IMPLEMENTS BEHING A WORKSHEET

I have noticed that despites the code compiles, the overall worksheet becomes unstable and tend to crash!
In additon the TypeOf function applied to the worksheet object that use the implements keyword, does not always behaves as you would expect.
Ex:
if you write on top of an excel worksheet module

Implements IEngine


Some time the test TypeOf sht is IEngine will return false even if it is implementing the interface.