When i create a meeting or appointment in my Outlook calendar I can set a "Show As" option.
If I select "Show As [Free]" it leaves my presence unchanged for the duration of the meeting.
If I select "Show As [Busy]" my Lync presence changes to "Busy" for the duration.
if I select "Show As [Out of Office]" my Lync presence remains, although the tiny purple OOF asterisk *does* show - if you look hard.
For consistency of user experience I suggest my Lync presence should change to grey to more properly reflect the 'OOF' state specified in the meeting.