When you have a star and invite someone who does not. If that person is at their limit for games, you get the same message you would get if you didn't have a star and were at your limit.
It's not too bad and when I see it again I'll know what I'm seeing. But it confused me enough at the time that I sent a message to Feedback saying Why am I still limited?
Maybe you should differentiate and say that the person you are challenging is at their limit... Just an idea.
The site overall is great!