src/Tools/jEdit/src/prover/Command.scala

 
   private var _status = Command.Status.UNPROCESSED
   def status = _status
   def status_=(st: Command.Status.Value) {
     if (st == Command.Status.UNPROCESSED) {
+      state_results.clear
       // delete markup
       for (child <- root_node.children) {
         child.children = Nil
       }
     }

 
   /* results */
 
   private val results = new mutable.ListBuffer[XML.Tree]
   private val state_results = new mutable.ListBuffer[XML.Tree]
-  def add_result(running: Boolean, tree: XML.Tree) {
+  def add_result(running: Boolean, tree: XML.Tree) = synchronized {
     (if (running) state_results else results) += tree
   }
 
   def result_document = XML.document(
     results.toList ::: state_results.toList match {