Group Access/Privacy settings - not working... why? HELP!

I have been testing out Group Privacy on my test site.  I created some content wich was gor Group Access only, and then logges on as a test user... I left the group, but even after logging out and upgrading I was stillable to log on as the user and see the private content.

This is a really serious issue. Has anyone else come across this?

Any help in resolving it would be VERY welcome.