Index: /trunk/src/org/openstreetmap/josm/gui/io/BasicUploadSettingsPanel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/io/BasicUploadSettingsPanel.java	(revision 17897)
+++ /trunk/src/org/openstreetmap/josm/gui/io/BasicUploadSettingsPanel.java	(revision 17898)
@@ -24,4 +24,5 @@
 import javax.swing.JPanel;
 import javax.swing.JTextField;
+import javax.swing.SwingUtilities;
 import javax.swing.event.AncestorEvent;
 import javax.swing.event.AncestorListener;
@@ -365,5 +366,5 @@
 
         private void setComment() {
-            destination.setComment(source.getText());
+            SwingUtilities.invokeLater(() -> destination.setComment(source.getText()));
         }