This bug was reported on Swing alias by Alan Snyder <javalists@cbfiddle.com>

The performance downgrade is rather big > 20x.

Test to benchmark the layout:
===================================

import javax.swing.JTextPane;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.Element;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.View;

public class Test {
 public static void main(String[] args) {
  boolean isRepeat = args.length > 0 && args[0].equals("repeat");
  new Test(isRepeat ? 1000 : 1);
 }

 public Test(int count) {
  TestRunner r = new TestRunner();
  for (int i = 0; i < 100; i++) {
   r.runTest();
  }
  for (int counter = 0; counter < count; counter++) {
   long ts1 = System.currentTimeMillis();
   for (int i = 0; i < 2000; i++) {
    r.runTest();
   }

   long ts2 = System.currentTimeMillis();
   System.err.println("Test: " + (ts2 - ts1) + " milliseconds");
  }
 }

 class TestRunner {
  View view;
  int counter;
  float width;
  float height;

  TestRunner() {
   try {
    DefaultStyledDocument doc = new DefaultStyledDocument();
    String text = createText();
    doc.insertString(0, text, new SimpleAttributeSet());
    Element p = doc.getParagraphElement(0);
    JTextPane pane = new JTextPane(doc);
    view = pane.getUI().getRootView(pane);
   } catch (BadLocationException ex) {
    throw new UnsupportedOperationException(ex);
   }
  }

  void runTest() {
   counter++;
   if (counter % 2 == 0) {
    width = 600;
    height = 600;
   } else {
    width = 800;
    height = 400;
   }
   view.setSize(width, height);
  }

  String createText() {
   String s = "Inserts some content into the document. Inserting content causes a write lock to be held while the actual changes are taking place, followed by notification to the observers on the thread that grabbed the write lock. ";
   return s + s + s + s + s + "\n";
  }
 }
}