The spec for
http://download.java.net/jdk7/docs/api/javax/swing/plaf/basic/BasicTreeUI.html#getPreferredSize(javax.swing.JComponent)

says

   "... this is a cover method for getPreferredSize(c, false)."

 There is a typo "checkConsistancy" -> "checkConsistEncy"

But the main problem is that this assertion is not satisfied by RI.
The call is delegated as (c, true), source code clearly shows that:
--- start BasicTreeUI.java ---
    /** Returns the preferred size to properly display the tree,
      * this is a cover method for getPreferredSize(c, false).
      */
    public Dimension getPreferredSize(JComponent c) {
        return getPreferredSize(c, true);
    }
--- end BasicTreeUI.java ---

This code is the same for JDK7, JDK6 and JDK5

Please see the following code sample as another illustration:

---
import javax.swing.*;
import javax.swing.plaf.basic.BasicLookAndFeel;
import javax.swing.plaf.basic.BasicTreeUI;
import java.awt.*;

public class Test {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(new BasicLookAndFeel() {
                        public String getName() { return "testName"; }
                        public String getID() { return "testID"; }
                        public String getDescription() { return "testDescription"; }
                        public boolean isNativeLookAndFeel() { return false; }
                        public boolean isSupportedLookAndFeel() { return true; }
                    });
                } catch (UnsupportedLookAndFeelException e) {
                    throw new RuntimeException(e);
                }

                JTree tree = new JTree();
                tree.setUI(
                        new BasicTreeUI() {
                            @Override
                            public Dimension getPreferredSize(JComponent c, boolean checkConsistency) {
                                System.out.println("Test.getPreferredSize(JComponent, boolean)");
                                System.out.println("checkConsistency = " + checkConsistency);
                                return super.getPreferredSize(c, checkConsistency);
                            }
                        }
                );
                tree.setPreferredSize(null);
                // call will be delegated to getPreferredSize(JComponent)
                tree.getPreferredSize();
            }
        });
    }
}
---

The output will be:

Test.getPreferredSize(JComponent, boolean)
checkConsistency = true