diff --git a/ganttzk/src/main/java/org/zkoss/ganttz/util/MutableTreeModel.java b/ganttzk/src/main/java/org/zkoss/ganttz/util/MutableTreeModel.java
index e04b0675c..97c07eccd 100644
--- a/ganttzk/src/main/java/org/zkoss/ganttz/util/MutableTreeModel.java
+++ b/ganttzk/src/main/java/org/zkoss/ganttz/util/MutableTreeModel.java
@@ -389,8 +389,7 @@ public class MutableTreeModel<T> extends AbstractTreeModel {
         Node<T> parentNode = find(parent);
         int[] changed = parentNode.down(find(node));
         if (changed.length != 0) {
-            fireEvent(parent, changed[0], changed[1],
-                    TreeDataEvent.CONTENTS_CHANGED);
+            fireRecreationOfInterval(parentNode, changed[0], changed[1]);
         }
     }
 
@@ -399,11 +398,18 @@ public class MutableTreeModel<T> extends AbstractTreeModel {
         Node<T> parentNode = find(parent);
         int[] changed = parentNode.up(find(node));
         if (changed.length != 0) {
-            fireEvent(parent, changed[0], changed[1],
-                    TreeDataEvent.CONTENTS_CHANGED);
+            fireRecreationOfInterval(parentNode, changed[0], changed[1]);
         }
     }
 
+    private void fireRecreationOfInterval(Node<T> parentNode, int start,
+            int endInclusive) {
+        fireEvent(parentNode.value, start, endInclusive,
+                TreeDataEvent.INTERVAL_REMOVED);
+        fireEvent(parentNode.value, start, endInclusive,
+                TreeDataEvent.INTERVAL_ADDED);
+    }
+
     public boolean isEmpty() {
         return getChildCount(getRoot()) == 0;
     }
diff --git a/ganttzk/src/test/java/org/zkoss/ganttz/util/MutableTreeModelTest.java b/ganttzk/src/test/java/org/zkoss/ganttz/util/MutableTreeModelTest.java
index c7aab141c..383a0f8a8 100644
--- a/ganttzk/src/test/java/org/zkoss/ganttz/util/MutableTreeModelTest.java
+++ b/ganttzk/src/test/java/org/zkoss/ganttz/util/MutableTreeModelTest.java
@@ -492,7 +492,7 @@ public class MutableTreeModelTest {
     }
 
     @Test
-    public void movingUpAndDownSendsEvents() {
+    public void movingUpAndDownSendsRemovalAndAddingEventsSoZKReloadsCorrectlyTheData() {
         final MutableTreeModel<Prueba> model = MutableTreeModel
                 .create(Prueba.class);
         Prueba prueba1 = new Prueba();
@@ -510,10 +510,14 @@ public class MutableTreeModelTest {
             }
         });
         model.up(prueba2);
-        checkIsValid(getLast(eventsFired), TreeDataEvent.CONTENTS_CHANGED,
+        checkIsValid(getPreviousToLast(eventsFired),
+                TreeDataEvent.INTERVAL_REMOVED, model.getRoot(), 0, 1);
+        checkIsValid(getLast(eventsFired), TreeDataEvent.INTERVAL_ADDED,
                 model.getRoot(), 0, 1);
         model.down(prueba1);
-        checkIsValid(getLast(eventsFired), TreeDataEvent.CONTENTS_CHANGED,
+        checkIsValid(getPreviousToLast(eventsFired),
+                TreeDataEvent.INTERVAL_REMOVED, model.getRoot(), 1, 2);
+        checkIsValid(getLast(eventsFired), TreeDataEvent.INTERVAL_ADDED,
                 model.getRoot(), 1, 2);
     }
 
@@ -579,6 +583,10 @@ public class MutableTreeModelTest {
         assertThat(event.getType(), equalTo(type));
     }
 
+    private TreeDataEvent getPreviousToLast(List<TreeDataEvent> list) {
+        return list.get(list.size() - 2);
+    }
+
     private TreeDataEvent getLast(List<TreeDataEvent> list) {
         if (list.isEmpty()) {
             throw new RuntimeException("no events");