Index: trunk/src/org/openstreetmap/josm/gui/layer/markerlayer/MarkerLayer.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/layer/markerlayer/MarkerLayer.java	(revision 5563)
+++ trunk/src/org/openstreetmap/josm/gui/layer/markerlayer/MarkerLayer.java	(revision 5564)
@@ -18,4 +18,6 @@
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 
@@ -199,4 +201,10 @@
         MarkerLayer layer = (MarkerLayer)from;
         data.addAll(layer.data);
+        Collections.sort(data, new Comparator<Marker>() {
+            @Override
+            public int compare(Marker o1, Marker o2) {
+                return Double.compare(o1.time, o2.time);
+            }
+        });
     }