Index: trunk/src/org/openstreetmap/josm/data/Preferences.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 6779)
+++ trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 6780)
@@ -1285,5 +1285,5 @@
         // See Oracle bug database: https://bugs.openjdk.java.net/browse/JDK-7075600
         // and https://bugs.openjdk.java.net/browse/JDK-6923200
-        if (Main.pref.getBoolean("jdk.Arrays.useLegacyMergeSort", !Version.getInstance().isLocalBuild())) {
+        if (getBoolean("jdk.Arrays.useLegacyMergeSort", !Version.getInstance().isLocalBuild())) {
             updateSystemProperty("java.util.Arrays.useLegacyMergeSort", "true");
         }
@@ -1292,5 +1292,6 @@
     private void updateSystemProperty(String key, String value) {
         if (value != null) {
-            System.setProperty(key, value);
+            String old = System.setProperty(key, value);
+            Main.debug("System property '"+key+"' set to '"+value+"'. Old value was '"+old+"'");
         }
     }
@@ -1299,9 +1300,9 @@
      * The default plugin site
      */
-    private final static String[] DEFAULT_PLUGIN_SITE = {
-    Main.JOSM_WEBSITE+"/plugin%<?plugins=>"};
-
-    /**
-     * Replies the collection of plugin site URLs from where plugin lists can be downloaded
+    private final static String[] DEFAULT_PLUGIN_SITE = {Main.JOSM_WEBSITE+"/plugin%<?plugins=>"};
+
+    /**
+     * Replies the collection of plugin site URLs from where plugin lists can be downloaded.
+     * @return the collection of plugin site URLs
      */
     public Collection<String> getPluginSites() {