Defender, I'm sorry but we cannot reproduce that.
When a user goes to the URL of a private group, he/she sees this message:
"We are sorry. This group is private." and the Avatar of the group creator.
Please provide the steps how to reproduce the issue. It would be great if you could that on our demo website.
I have made a widget for all users with links to my closed groups. I am using Hint plugin and here is the follow button. Yes I can uncheck the follow, I can hide my closed groups, but it is not a good solution I think.