I have noticed lately when I am online and I have my online status set to "show offline", it will for a few minutes and then out of no where it will show be online doing the same thing I was doing when I changed the setting.
This happen last night to me and a friend of mine. We were in a party chat and both of us were showing offline. Then I get a notification that he is online and just a few mintues after that he said it showed me getting online. I tried to search around a bit for this but couldn't find anything. I have also noticed people showing online playing a game and they are not online at all.