diff -r 7ada6dfa9ab5 -r 4e4b56b7a3a5 src/HOL/Tools/Sledgehammer/sledgehammer_isar.ML
--- a/src/HOL/Tools/Sledgehammer/sledgehammer_isar.ML	Wed Mar 27 17:55:21 2013 +0100
+++ b/src/HOL/Tools/Sledgehammer/sledgehammer_isar.ML	Wed Mar 27 17:58:07 2013 +0100
@@ -419,6 +419,7 @@
   end
 
 fun sledgehammer_trans (((subcommand, params), fact_override), opt_i) =
+  Toplevel.unknown_proof o
   Toplevel.keep (hammer_away params subcommand opt_i fact_override
                  o Toplevel.proof_of)