Has any other admin seen this pop up?
I've had half a dozen users ask about "Why doesn't my calendar show me busy?" or "People keep scheduling meetings when I'm clearly busy! What's up?"
It turns out if you log into webmail - these were users that NEVER go into webmail - the box has been checked.
These are all iOS and OS X (Mail, Calendar) users.
I can't figure out what causes it, and it seems totally random.
This has existed since NE 8 - currently on NE 8.0.3