src/Tools/jEdit/src/prover/MarkupNode.scala

   }
 
   private def remove(nodes : List[MarkupNode]) {
     children_cell = children diff nodes
 
-    for(node <- nodes) swing_node remove node.swing_node
+      for(node <- nodes) try {
+        swing_node remove node.swing_node
+      } catch { case e : IllegalArgumentException =>
+        System.err.println(e.toString)
+        case e => throw e
+      }
   }
 
   def dfs : List[MarkupNode] = {
     var all = Nil : List[MarkupNode]
     for(child <- children)