I thought it could have been to do with the different "Show this includelet to" settings available for the Custom Content includelet. Where you can configure it to only show to logged in users, for example.

However, I just created a test page with a custom content includelet with each of the visibility settings, and tried it when logged in and logged out etc and can't get it to redirect to the login page.

So, if you're still having problems, could you let me know the URL of the page and I will look into it some more.

Thanks

Joe