I was talking with some guild mates on this subject and no one really had a clear answer.

How exactly does invisibility guard work (if at all) for defenses? Does it only affect a mobs ability to see you and therefore target you? Or does it apply a concealment affect that does not appear in the combat log? Does it do both?

I would imagine it would apply a concealment effect on attackers but it doesn't appear to do so.

Any legitimate clarification would be helpful, especially now that indivisibility in general has been addressed.