diff -r cea207576f81 -r e8c1c5612677 src/Tools/quickcheck.ML
--- a/src/Tools/quickcheck.ML	Sat Jul 13 13:58:13 2013 +0200
+++ b/src/Tools/quickcheck.ML	Sat Jul 13 14:11:48 2013 +0200
@@ -94,7 +94,7 @@
 
 val _ =
   ProofGeneral.preference_option ProofGeneral.category_tracing
-    (SOME "true")
+    NONE
     @{option auto_quickcheck}
     "auto-quickcheck"
     "Run Quickcheck automatically";