Index: src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java
===================================================================
--- src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java	(revision 6091)
+++ src/org/openstreetmap/josm/gui/dialogs/properties/TagEditHelper.java	(working copy)
@@ -52,6 +52,7 @@
 import javax.swing.JPanel;
 import javax.swing.JPopupMenu;
 import javax.swing.KeyStroke;
+import javax.swing.SwingUtilities;
 import javax.swing.table.DefaultTableModel;
 import javax.swing.text.JTextComponent;
 
@@ -693,7 +694,11 @@
                             // add tags and close window on double-click
                             if (e.getClickCount()>1) {
                                 performTagAdding();
-                                buttonAction(0, null); // emulate OK click and close the dialog
+                                SwingUtilities.invokeLater(new Runnable() {
+                                    @Override public void run() {
+                                        buttonAction(0, null); // emulate OK click and close the dialog
+                                    }
+                                });
                             }
                             // add tags on Shift-Click
                             if (e.isShiftDown()) {