src/Pure/PIDE/prover.scala

 
     override def toString: String =
     {
       val res =
         if (is_status || is_report) message.body.map(_.toString).mkString
-        else Pretty.string_of(message.body)
+        else Pretty.string_of(message.body, metric = Symbol.Metric)
       if (properties.isEmpty)
         kind.toString + " [[" + res + "]]"
       else
         kind.toString + " " +
           (for ((x, y) <- properties) yield x + "=" + y).mkString("{", ",", "}") + " [[" + res + "]]"