Grouper 2.0 has web services changes which are not backwards compatible. This is the first time Grouper web services has this issue. The part that isnt backwards compatible is sending back another attribute on an object that clients with a previous version are not expecting (e.g. if the attribute assignment is disallowed, or what the limits are on a permission).
Grouper RESTlike is automatic based on Javabean, but the marshaling will not marshal null data. The Grouper WS client passes in its version, and if it is less than 2.0, the new fields will be null, and the response is backwards compatible.