Index: trunk/src/org/openstreetmap/josm/gui/dialogs/changeset/ChangesetDiscussionPanel.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/dialogs/changeset/ChangesetDiscussionPanel.java	(revision 17505)
+++ trunk/src/org/openstreetmap/josm/gui/dialogs/changeset/ChangesetDiscussionPanel.java	(revision 17506)
@@ -124,9 +124,10 @@
             try {
                 OsmApi.getOsmApi().addCommentToChangeset(current, dialog.getInputText(), null);
-            } catch (OsmTransferException e) {
+                actUpdateChangesets.actionPerformed(null);
+            } catch (OsmTransferException | IllegalArgumentException e) {
                 Logging.error(e);
                 JOptionPane.showMessageDialog(
                         MainApplication.getMainFrame(),
-                        ExceptionUtil.explainOsmTransferException(e),
+                        ExceptionUtil.explainException(e),
                         tr("Error"),
                         JOptionPane.ERROR_MESSAGE);
Index: trunk/src/org/openstreetmap/josm/io/OsmApi.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/OsmApi.java	(revision 17505)
+++ trunk/src/org/openstreetmap/josm/io/OsmApi.java	(revision 17506)
@@ -550,6 +550,6 @@
         else if (changeset.getId() <= 0)
             throw new IllegalArgumentException(tr("Changeset ID > 0 expected. Got {0}.", changeset.getId()));
-        sendRequest("POST", "changeset/" + changeset.getId() + "/comment",
-                "text=" + Utils.encodeUrl(comment), monitor, "application/x-www-form-urlencoded", true, false);
+        sendRequest("POST", "changeset/" + changeset.getId() + "/comment?text="+ Utils.encodeUrl(comment),
+                null, monitor, "application/x-www-form-urlencoded", true, false);
     }