src/Pure/System/session.scala

--- a/src/Pure/System/session.scala	Mon Jul 29 14:18:57 2013 +0200
+++ b/src/Pure/System/session.scala	Mon Jul 29 14:37:59 2013 +0200
@@ -461,7 +461,7 @@
             if (rc == 0) phase = Session.Inactive
             else phase = Session.Failed
 
-          case _ => bad_output()
+          case _ => raw_output_messages.event(output)
         }
       }
     }