src/Tools/jEdit/src/proofdocument/ProofDocument.scala

 
       invalid_tokens = invalid_tokens dropWhile (stop(_) < stop(new_token))
       invalid_tokens match {
         case t::ts => if(start(t) == start(new_token) &&
                          start(t) > change.start + change.added.length) {
-          old_suffix = ts
+          old_suffix = t::ts
+          new_tokens = new_tokens.tail
           invalid_tokens = Nil
         }
         case _ =>
       }
     }