FULL PRODUCT VERSION :
Product Version: NetBeans IDE 6.9 (Build 201006101454)
Java: 1.6.0_10; Java HotSpot(TM) Client VM 11.0-b15
System: Windows XP version 5.1 running on x86; Cp1252; en_US (nb)
Userdir: C:\Documents and Settings\danny.rich\.netbeans\6.9

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows ver 2002 service pack 2

A DESCRIPTION OF THE PROBLEM :
First application of JFileChooser shows the File & Directory window with the filename box empty. Second application retains the last used file name & extension, even if the previous extension is not consistent with the currently active extension filter.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create JFileChooser dialog
Set File extension filter
Show OpenDialog
Change File extension filter
Show SaveDialog
{Opened file name & extension are shown in the Save file name textbox}

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Either the SaveDialog file name textbox should be set to NULL as at first or the extension of the retained filename should be changed to the FileExtensionFilter value.
ACTUAL -
A SaveDialog with filter for .CXF extension showed a filename with MIF extension. This is a potential error for the user that will overwrite the first file with modified data.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
private void openMIFActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        FileNameExtensionFilter filter = new FileNameExtensionFilter("MIF Files","mif");
        fileChooser.addChoosableFileFilter(filter);
        int retValue = fileChooser.showOpenDialog(this.getFrame());
        if (retValue == fileChooser.APPROVE_OPTION) {
// Open the MIF file checking for IOExceptions
            try {
                File mifFile = fileChooser.getSelectedFile();
                Scanner scan = new Scanner(mifFile);

<snip>

private void convertMIFActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
// Create the CXF file to accept the color standard data from the MIF file
        FileNameExtensionFilter filter = new FileNameExtensionFilter("CXF Files","cxf");
        fileChooser.addChoosableFileFilter(filter);
        int retValue = fileChooser.showSaveDialog(this.getFrame());
        if (retValue == fileChooser.APPROVE_OPTION) {
            PrintWriter cxfOut = null;
            NumberFormat nfmt = new DecimalFormat("####.#####");
// CXF is a form of XML without DTD or data definition or validation rules
// Create and open the file looking for IOExceptions
// Much of the content of a CXF file is fixed data.
// This conversion uses CXF v1.0 which has the simplest format
            try {
                File cxfFile = fileChooser.getSelectedFile();
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
User must manually enter the new filename and extension or at the very least delete the old extension and enter the new extension.