Step to reproduce
-------------------
1) Run the below program.
2) you will a frame containing a vertical splite pane. JTextArea is set as the top component of the splitepane & JLabeltowards is set to the bottom of splitepane.
3) drag the divider to the middle of the frame.
4) Change the theme . Observe that splitepane divider is automatically set to the minimum size or as the frame is first realized. If you see the same then the bug is reproduce.
I tested this in tiger & jdk6.0 & jdk7.0 & it reproducable.

Source code begin
------------------
import java.awt.BorderLayout;
import java.awt.Dimension;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class SplitPaneBug implements Runnable {
public static final void main(String[] args) {
SwingUtilities.invokeLater(new SplitPaneBug());
}

public void run() {
JTextArea textArea = new JTextArea();
for (int i = 0; i < 100; i ++) {
if (i > 0) {
textArea.append("\n");
}
textArea.append("Line " + (i + 1));
}
JScrollPane scroll = new JScrollPane(textArea);
JLabel label = new JLabel("", JLabel.CENTER);
JSplitPane split = new JSplitPane(JSplitPane.VERTICAL_SPLIT);
split.setTopComponent(scroll);
split.setBottomComponent(label);
JComponent content = new JPanel(new BorderLayout());
content.add(split, BorderLayout.CENTER);
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setContentPane(content);
f.pack();
f.setSize(new Dimension(600, 600));
f.setLocationRelativeTo(null);
f.setVisible(true);
label.setText("The split pane layout gives this label " + (label.getSize().height - label.getPreferredSize().height) + "px of height it doesn't need.");
}
}
----
end