diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java b/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
index ffc56b6..b4acd60 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java
@@ -727,6 +727,10 @@
         getRefBounds2(mTempRect);
         t.setPosition(leash2, mTempRect.left, mTempRect.top)
                 .setWindowCrop(leash2, mTempRect.width(), mTempRect.height());
+        // Make right or bottom side surface always higher than left or top side to avoid weird
+        // animation when dismiss split. e.g. App surface fling above on decor surface.
+        t.setLayer(leash1, 1);
+        t.setLayer(leash2, 2);
 
         if (mImePositionProcessor.adjustSurfaceLayoutForIme(
                 t, dividerLeash, leash1, leash2, dimLayer1, dimLayer2)) {
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
index a841b7f..d6f4d6d 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java
@@ -220,12 +220,20 @@
                 mCallbacks.onNoLongerSupportMultiWindow();
                 return;
             }
-            mChildrenTaskInfo.put(taskInfo.taskId, taskInfo);
+            if (taskInfo.topActivity == null && mChildrenTaskInfo.contains(taskInfo.taskId)
+                    && mChildrenTaskInfo.get(taskInfo.taskId).topActivity != null) {
+                // If top activity become null, it means the task is about to vanish, we use this
+                // signal to remove it from children list earlier for smooth dismiss transition.
+                mChildrenTaskInfo.remove(taskInfo.taskId);
+                mChildrenLeashes.remove(taskInfo.taskId);
+            } else {
+                mChildrenTaskInfo.put(taskInfo.taskId, taskInfo);
+            }
             mCallbacks.onChildTaskStatusChanged(taskInfo.taskId, true /* present */,
                     taskInfo.isVisible);
-            if (!ENABLE_SHELL_TRANSITIONS) {
-                updateChildTaskSurface(
-                        taskInfo, mChildrenLeashes.get(taskInfo.taskId), false /* firstAppeared */);
+            if (!ENABLE_SHELL_TRANSITIONS && mChildrenLeashes.contains(taskInfo.taskId)) {
+                updateChildTaskSurface(taskInfo, mChildrenLeashes.get(taskInfo.taskId),
+                        false /* firstAppeared */);
             }
         } else {
             throw new IllegalArgumentException(this + "\n Unknown task: " + taskInfo