Index: /trunk/src/org/openstreetmap/josm/data/Preferences.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 9311)
+++ /trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 9312)
@@ -965,4 +965,6 @@
                 save();
             } else if (reset) {
+                File backupFile = new File(prefDir, "preferences.xml.bak");
+                Main.platform.rename(preferenceFile, backupFile);
                 Main.warn(tr("Replacing existing preference file ''{0}'' with default preference file.", preferenceFile.getAbsoluteFile()));
                 resetToDefault();