Andreas Raab wrote:

>Because of a bug in a feature that tries to warn you if you define a new
>class with the name of an existing one (e.g., inadvertently trying to
>define your own class "Button" or somesuch). There seems to be a bug in
>the form that the identification of whether you "define a new class"
>(bad) or "redefine the existing class" (okay) fails for the case of meta
>classes.
>
>Cheers,
>  - Andreas
>  
>

To reiterate (in case you missed it):

When you are only adding a class instance variable, and it comes up with 
that warning dialog, you can ignore the warning.

Nevin