Global IDs showing up incorrectly in REST Query operation

[JonFisher]

I have a map service pointing to a dataset with a GLOBALID field. The field is clearly populated with valid values in the data, and the field comes through fine when viewing the map service in ArcMap:
http://maps.tnc.org/ecadpubprod-anon/rest/services/tnc_lands_anon/MapServer?f=lyr

However, when I query the map service (either via the REST interface or via a flex app), the GLOBALID values all show up as {00000000-0000-0000-0000-000000000000} (all 0) instead of the actual values:
http://maps.tnc.org/ecadpubprod-anon/rest/services/tnc_lands_anon/MapServer/1/query?text=&geometry=&...

This seems like it should be impossible, the data is right, the map service is right in ArcMap, so how is it getting scrambled? And why only for this data set? The points layer in the same map service also has a globalid and it works fine...