FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)


ADDITIONAL OS VERSION INFORMATION :
Linux 2.6.17-10-generic (using GTK)

A DESCRIPTION OF THE PROBLEM :
After setting the file selection mode of a JFileChooser object to JFileChooser.DIRECTORIES_ONLY, the UI will change so that only directories are displayed. However, if JFileChooser.FILES_ONLY is set as the file selection mode afterwards, the UI will not change and the user will only be able to traverse through directories and not see or choose any files.

This problem only occurs when using the system look and feel on a Linux machine using GTK 2.0.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Set the look and feel to the system look and feel.
Create a new JFileChooser

Set its file selection mode to JFileChooser.FILES_ONLY
Display the JFileChooser

Set its the file selection mode to JFileChooser.DIRECTORIES_ONLY
Display the JFileChooser

Set its file selection mode to JFileChooser.FILES_ONLY
Display the JFileChooser

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A file chooser dialog should appear, with two columns. One column for selecting directories and another for selecting files.

After the user closes the dialog, it should reappear, however this time with only one column. The column should display directories only.

After the user closes the dialog again, it should reappear again. This time with two columns, as it was originally. One column for selecting directories and another for selecting files.
ACTUAL -
A file chooser dialog appears, with two columns. One column for selecting directories and another for selecting files.

After the dialog is closed, it reappears, however this time with only one column. The column displays directories only.

After the dialog is closed, it reappears again. However, even though its file selection mode is set to files and directories, the UI is the exact same as it was previously, when only directories were shown.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;

public class Test {

public static void main(String[] args) throws Exception {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
JFileChooser fileChooser = new JFileChooser();

fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
fileChooser.showOpenDialog(null);

fileChooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
fileChooser.showOpenDialog(null);

fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
fileChooser.showOpenDialog(null);
}

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use a separate JFileChooser for selecting directories only.