Index: /trunk/src/org/openstreetmap/josm/data/Preferences.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 5899)
+++ /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 5900)
@@ -1328,5 +1328,5 @@
      */
     public void updateSystemProperties() {
-        if(getBoolean("prefer.ipv6", true)) {
+        if(getBoolean("prefer.ipv6", false)) {
             // never set this to false, only true!
             updateSystemProperty("java.net.preferIPv6Addresses", "true");