=== modified file 'mail/mail_thread.py'
--- mail/mail_thread.py	2014-04-16 14:37:55 +0000
+++ mail/mail_thread.py	2014-05-10 16:21:34 +0000
@@ -1567,7 +1567,7 @@
             # done with SUPERUSER_ID, because on some models users can post only with read access, not necessarily write access
             self.write(cr, SUPERUSER_ID, [thread_id], {'message_last_post': fields.datetime.now()}, context=context)
         message = mail_message.browse(cr, uid, msg_id, context=context)
-        if message.author_id and thread_id and type != 'notification' and not context.get('mail_create_nosubscribe'):
+        if model != 'mail.group' and message.author_id and thread_id and type != 'notification' and not context.get('mail_create_nosubscribe'):
             self.message_subscribe(cr, uid, [thread_id], [message.author_id.id], context=context)
         return msg_id