This particular issue is actually not so much a group permission bug but it's a tagging bug. Right now, if private content is tagged, it will still appear as related content in public forum areas. Users who do NOT have permissions to that forum won't be able to read the thread (they'll get a grey screen) but they can see the title. The short term solution is simply to leave private content untagged. In this case, Dawgcatching started a thread in the Advisory forum and because he's an Industry Insider, it was automatically tagged Dawgcatching. I untagged it so his threads shouldn't be showing up in public areas. We're working on this bug in the very near term.