Index: src/org/openstreetmap/josm/gui/MapFrame.java
===================================================================
--- src/org/openstreetmap/josm/gui/MapFrame.java	(revision 15951)
+++ src/org/openstreetmap/josm/gui/MapFrame.java	(working copy)
@@ -342,6 +342,7 @@
         MainApplication.getLayerManager().removeLayerChangeListener(this);
         MainApplication.getLayerManager().removeActiveLayerChangeListener(this);
         MainApplication.getMenu().modeMenu.removeAll();
+        rememberToggleDialogWidth();
         dialogsPanel.destroy();
         Config.getPref().removePreferenceChangeListener(sidetoolbarPreferencesChangedListener);
         for (int i = 0; i < toolBarActions.getComponentCount(); ++i) {
@@ -738,7 +739,7 @@
      */
     public void rememberToggleDialogWidth() {
         if (dialogsPanel.isVisible()) {
-            TOGGLE_DIALOGS_WIDTH.put(splitPane.getWidth() - splitPane.getDividerLocation());
+            TOGGLE_DIALOGS_WIDTH.put(splitPane.getWidth() - splitPane.getDividerLocation() - splitPane.getDividerSize() - 1);
         }
     }