Inconsistent performance applying ForegroundActions in a JEditorPane when reading HTML

Using the sscce below, I am unable to reproduce the effect you describe. Such anomalies may arise if Swing GUI objects are not constructed and manipulated only on the event dispatch thread. The example uses EventQueue.invokeLater() accordingly.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JToolBar;
import javax.swing.text.StyledEditorKit;
import javax.swing.text.html.HTMLEditorKit;

/** http://stackoverflow.com/questions/8523445 */
public class StyledEditorTest extends JFrame {

    public StyledEditorTest() {
        JEditorPane editorPane = new JEditorPane();
        editorPane.setContentType("text/HTML");
        editorPane.setEditorKit(new HTMLEditorKit());
        editorPane.setText("<hr>Welcome to <b>StackOverFlow!</b><hr>");
        JToolBar bar = new JToolBar();
        bar.add(new StyledEditorKit.ForegroundAction("Red", Color.red));
        bar.add(new StyledEditorKit.ForegroundAction("Blue", Color.blue));
        bar.add(new StyledEditorKit.FontSizeAction("12", 12));
        bar.add(new StyledEditorKit.FontSizeAction("14", 14));
        bar.add(new StyledEditorKit.FontSizeAction("16", 16));
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
        this.add(bar, BorderLayout.NORTH);
        this.add(editorPane, BorderLayout.CENTER);
        this.pack();
        this.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new StyledEditorTest();
            }
        });
    }
}