Java.utils.prefs.Preferences API throws exception on Mac, not Windows

Question

This is a Mac-specific problem. Is it a bug, or am I misusing the java.utils.prefs.Preferences API?
The Preferences flush() API call always throws a BackingStoreException if a system tree preferences root has been read. The system tree has not been modified or written to, but the flush() call is nevertheless throwing an exception. This occurs when running as a normal user without the ability to write to /Library/Preferences.
See sample code below. Note that I only want to read the system prefs tree. The user tree write flush fails. If the system tree node is not created, the user flush() succeeds.
Steps to Reproduce
Delete any existing Java prefs files:
~/Library/Preferences/com.apple.java.util.prefs.plist
~/Library/Preferences/com.mycompany.prefstest
/Library/Preferences/com.apple.java.util.prefs.plist
/Library/Preferences/com.mycompany.prefstest
Run the following Java code:
package com.mycompany.prefstest;
import java.util.prefs.BackingStoreException;
import java.util.prefs.Preferences;
public class PrefsTest {
      * @param args
     public static void main(String[] args) {
          String strKey1 = "com/mycompany/prefstest/one/two/three/four/key1";
          Preferences systemRoot = Preferences.systemRoot();
          Preferences userRoot = Preferences.userRoot();
          // Get a value for user prefs.
          String value1 = userRoot.get(strKey1, "missing");
          // Fall back to system prefs if it is not defined.
          if (value1.equals("missing"))
               value1 = systemRoot.get(strKey1, "missing");
          System.out.println("key1 --> " + value1);
          // If still not defined, set a user-specific value
          if (value1.equals("missing"))
               userRoot.put(strKey1, "value1");
               try {
                    userRoot.flush();
                    System.out.println("flushed prefs successfully");
               catch (BackingStoreException e)
                    System.out.println("Exception: " + e.toString());
Expected Results
Should produce the output:
key --> missing
flushed prefs successfully
Actual Results
Console output is
key --> missing
Exception: java.util.prefs.BackingStoreException: Synchronization failed for node '/'
Notes
$ java -version
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11-402-11D50b)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02-402, mixed mode)
also tested with:
java version "1.7.0_04-ea"
Java(TM) SE Runtime Environment (build 1.7.0_04-ea-b16)
Java HotSpot(TM) 64-Bit Server VM (build 23.0-b17, mixed mode)
Mac OS X 10.7.3.
The "Expected Results" are correctly obtained running the same code on MS-Windows.
Running the jar as sudo works (with write access to /Library/Preferences), as expected.

Answer 1

Just for fun, try a key without slashes in it (but for example dots if you must use such a long key).
I say that because a quick Google search points out that Apple stores the preferences in a file hierarchy in the user home folder. I can already see how using keys which look like a file path are going to cause nuclear reactors to meltdown...