Why can demo users not have a unique validation on the account entity?

Hi, For ease of use I have my demo users turned on. For some reason it doesn't allow me to have a unique validation rule on the account entity. this is only for demo users. Just out of curiousity, why is it like that?  
1 answers

The error message is a bit confusing: the problem is that you have a unique validation on User entity and on it's subentity Account. You cannot have the same validation twice on an attribute.