I think I’ve found a bug in Word 2013 and Word 2013 SP1 when using SharePoint 2013 and SharePoint 2013 SP1.
When the Document Information Panel is used in a Word Document, it doesn’t support Lookup columns. Wherever there is a lookup column, Word just says “Currently Unavailable”.
Loading the exact same document in Word 2010 results in the Document Information Panel showing the correct options for all fields. So I think this isn't a configuraiton error, but a bug in Word 2013.
Strangely, if I use Word 2013 insert a Quick Part to lookup "ClassificationZ" the quick part works (see screenshot), but the Document Information Panel remains as “Currently Unavailable” for ClassificationZ.
I’ve been able to recreate this in 2 totally separate environments.
Can anybody else reproduce? Any ideas what’s going on? Puzzled....