FULL PRODUCT VERSION :
java version "1.8.0_151"
Java(TM) SE Runtime Environment (build 1.8.0_151-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.151-b12, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
The wrapping of text chunks with different attributes (styled fragments) works incorrectly.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached code and start typing at the beginning of the document (the empty line above the preset text).

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No changes in second paragraphs wrapping.
ACTUAL -
With every typed letter the wrapping of the second paragraph changes.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.awt.BorderLayout;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;

public class BugWrapJava7 extends JFrame {

    JTextPane jtp;
    StyledDocument doc;

    public BugWrapJava7() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        jtp = new JTextPane();
        add(jtp, BorderLayout.CENTER);
        jtp.setText("\ntype some text in the above empty line and check the wrapping behavior");
        doc = jtp.getStyledDocument();
        doc.addDocumentListener(new DocumentListener() {
            public void insertUpdate(DocumentEvent e) {
                insert();
            }
            public void removeUpdate(DocumentEvent e) {
            }
            public void changedUpdate(DocumentEvent e) {
            }
        });
        setSize(200, 200);
        setVisible(true);
    }
    public void insert() {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                Style defaultStyle = jtp.getStyle(StyleContext.DEFAULT_STYLE);
                doc.setCharacterAttributes(0, doc.getLength(), defaultStyle, false);
            }
        });
    }
    public static void main(String[] args) {
        new BugWrapJava7();
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
A workaround was posted on "http://java-sl.com/tip_java7_text_wrapping_bug_fix.html", but it slows down to much with large texts (up to 50-60 pages).