Index: /trunk/src/org/openstreetmap/josm/gui/dialogs/LayerListPopup.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/dialogs/LayerListPopup.java	(revision 17997)
+++ /trunk/src/org/openstreetmap/josm/gui/dialogs/LayerListPopup.java	(revision 17998)
@@ -2,4 +2,6 @@
 package org.openstreetmap.josm.gui.dialogs;
 
+import static java.util.Collections.emptyList;
+import static java.util.stream.Collectors.toCollection;
 import static org.openstreetmap.josm.gui.help.HelpUtil.ht;
 import static org.openstreetmap.josm.tools.I18n.tr;
@@ -9,7 +11,6 @@
 import java.awt.event.ActionEvent;
 import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
+import java.util.stream.Stream;
 
 import javax.swing.AbstractAction;
@@ -82,5 +83,6 @@
         if (selectedLayers.size() == 1) {
             Action[] entries = selectedLayers.get(0).getMenuEntries();
-            actions = entries != null ? Arrays.asList(entries) : Collections.emptyList();
+            // Since we may add to the array later, we cannot use Arrays.asList -- it prohibits the use of `add` or `remove`.
+            actions = entries != null ? Stream.of(entries).collect(toCollection(ArrayList::new)) : emptyList();
         } else {
             // Very simple algorithm - first selected layer has actions order as in getMenuEntries, actions from other layers go to the end