diff -r e27cfd2bf094 -r 0d4ee4168e41 src/Pure/System/invoke_scala.scala
--- a/src/Pure/System/invoke_scala.scala	Tue Nov 03 11:24:42 2015 +0100
+++ b/src/Pure/System/invoke_scala.scala	Tue Nov 03 13:54:34 2015 +0100
@@ -94,7 +94,7 @@
     msg.properties match {
       case Markup.Invoke_Scala(name, id) =>
         futures += (id ->
-          Simple_Thread.submit_task {
+          Standard_Thread.submit_task {
             val (tag, result) = Invoke_Scala.method(name, msg.text)
             fulfill(prover, id, tag, result)
           })