It was:
$paths/selected_directory/another_selected_directory(or file)
and a normal behavior of the JFileChooser GUI.

If you notice, when you first click the directory, the name appears in
the text field.
When you double click, you enter that directory, but the name stays in
the text field.

The name staying in the text field is definitely what causes your
described behavior.
<sscce>
import javax.swing.*;
public class FileChoo {
   public static void main(String[] args) {
       final JFileChooser jFileChooser = new JFileChooser();

jFileChooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
       jFileChooser.showOpenDialog(null);
       System.out.println("file = " +
jFileChooser.getSelectedFile());
   }
}
</sscce>

If it is
$paths/selected_directory/another_selected_directory_or_file
that is a normal behavior of the JFileChooser GUI.

JFileChooser is broken in many twisted ways. Sun says this is how it
has to be and closed all related bug reports.