A new version of Chapter 5 of the Personnel Policy Guidance  (Updated Procedural Guidance in Support of Active Army (AA) Stop Loss/Stop) reports that a new MILPER Message has been issued, MILPER Message 05-303 .

(If you view the PPG chapter as HTML rather than as a PDF, it has a link to it.) 
Please note: The old MILPER Message (04-169 at 1. 5.) says that those on transition leave are not subject to stop loss.