Index: /trunk/.classpath
===================================================================
--- /trunk/.classpath	(revision 12877)
+++ /trunk/.classpath	(revision 12878)
@@ -31,5 +31,5 @@
 	<classpathentry kind="lib" path="test/lib/fest/debug-1.0.jar"/>
 	<classpathentry exported="true" kind="con" path="GROOVY_DSL_SUPPORT"/>
-	<classpathentry kind="lib" path="tools/spotbugs/spotbugs-annotations.jar"/>
+	<classpathentry exported="true" kind="lib" path="tools/spotbugs/spotbugs-annotations.jar"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>
Index: /trunk/src/org/openstreetmap/josm/gui/download/DownloadDialog.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/download/DownloadDialog.java	(revision 12877)
+++ /trunk/src/org/openstreetmap/josm/gui/download/DownloadDialog.java	(revision 12878)
@@ -55,4 +55,5 @@
 import org.openstreetmap.josm.tools.InputMapUtils;
 import org.openstreetmap.josm.tools.JosmRuntimeException;
+import org.openstreetmap.josm.tools.ListenerList;
 import org.openstreetmap.josm.tools.Logging;
 import org.openstreetmap.josm.tools.OsmUrlToBounds;
@@ -84,5 +85,12 @@
     }
 
-    protected final transient List<DownloadSource<?>> downloadSources = new ArrayList<>();
+    protected static final ListenerList<DownloadSourceListener> downloadSourcesListeners = ListenerList.create();
+    protected static final List<DownloadSource<?>> downloadSources = new ArrayList<>();
+    static {
+        // add default download sources
+        addDownloadSource(new OSMDownloadSource());
+        addDownloadSource(new OverpassDownloadSource());
+    }
+
     protected final transient List<DownloadSelection> downloadSelections = new ArrayList<>();
     protected final JTabbedPane tpDownloadAreaSelectors = new JTabbedPane();
@@ -114,8 +122,4 @@
     protected final JPanel buildMainPanel() {
         mainPanel = new JPanel(new GridBagLayout());
-
-        // add default download sources
-        addDownloadSource(new OSMDownloadSource());
-        addDownloadSource(new OverpassDownloadSource());
 
         // must be created before hook
@@ -335,6 +339,7 @@
      * @throws JosmRuntimeException If the download source is already added. Note, download sources are
      * compared by their reference.
-     */
-    public <T> void addDownloadSource(DownloadSource<T> downloadSource) {
+     * @since 12878
+     */
+    public static <T> void addDownloadSource(DownloadSource<T> downloadSource) {
         if (downloadSources.contains(downloadSource)) {
             throw new JosmRuntimeException("The download source you are trying to add already exists.");
@@ -342,5 +347,5 @@
 
         downloadSources.add(downloadSource);
-        addNewDownloadSourceTab(downloadSource);
+        downloadSourcesListeners.fireEvent(l -> l.downloadSourceAdded(downloadSource));
     }
 
@@ -581,6 +586,11 @@
      * @since 12706
      */
-    private static class DownloadSourceTabs extends JTabbedPane {
+    private static class DownloadSourceTabs extends JTabbedPane implements DownloadSourceListener {
         private final List<AbstractDownloadSourcePanel<?>> allPanels = new ArrayList<>();
+
+        DownloadSourceTabs() {
+            downloadSources.forEach(this::downloadSourceAdded);
+            downloadSourcesListeners.addListener(this);
+        }
 
         List<AbstractDownloadSourcePanel<?>> getAllPanels() {
@@ -631,4 +641,9 @@
             }
             super.insertTab(title, icon, component, tip, index);
+        }
+
+        @Override
+        public void downloadSourceAdded(DownloadSource<?> source) {
+            addPanel(source.createPanel());
         }
     }
Index: /trunk/src/org/openstreetmap/josm/gui/download/DownloadSourceListener.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/download/DownloadSourceListener.java	(revision 12878)
+++ /trunk/src/org/openstreetmap/josm/gui/download/DownloadSourceListener.java	(revision 12878)
@@ -0,0 +1,15 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.gui.download;
+
+/**
+ * Listener to get notified about changes in the list of download sources.
+ * @since 12878
+ */
+interface DownloadSourceListener {
+
+    /**
+     * Called when a download source has been added.
+     * @param source the new added download source.
+     */
+    void downloadSourceAdded(DownloadSource<?> source);
+}