src/Pure/Thy/thy_syntax.scala

     node: Document.Node, edit: Document.Edit_Text): Document.Node =
   {
     edit match {
       case (_, Document.Node.Clear()) => node.clear
 
+      case (_, Document.Node.Blob()) => node
+
       case (name, Document.Node.Edits(text_edits)) =>
         val commands0 = node.commands
         val commands1 = edit_text(text_edits, commands0)
         val commands2 =
           recover_spans(thy_load, syntax, doc_blobs, name, node.perspective.visible, commands1)

         if (node.same_perspective(perspective)) node
         else
           node.update_perspective(perspective).update_commands(
             consolidate_spans(thy_load, syntax, doc_blobs, reparse_limit,
               name, visible, node.commands))
-
-      case (_, Document.Node.Blob()) => node
     }
   }
 
   def text_edits(
       thy_load: Thy_Load,