[BUG]Load Timeline Asset from Assetbundle

Code (CSharp):

1. public class ZTest : MonoBehaviour {
2.     AssetBundle assetBundleP = null;
3.     AssetBundle assetBundleT = null;
4.  
5.     private void OnGUI() {
6.         #region stepA
7.         if (GUILayout.Button("Load AB_T", GUILayout.Width(200), GUILayout.Height(150))) {
8.             string path = Path.Combine(Application.streamingAssetsPath, "Android/testtimeline");
9.             Debug.Log("path " + path);
10.             assetBundleT = AssetBundle.LoadFromFile(path);
11.         }
12.         #endregion
13.  
14.         #region stepB
15.         if (GUILayout.Button("Load AB_P", GUILayout.Width(200), GUILayout.Height(150))) {
16.             string path = Path.Combine(Application.streamingAssetsPath, "Android/playabledirector");
17.             Debug.Log("path " + path);
18.             assetBundleP = AssetBundle.LoadFromFile(path);
19.         }
20.         #endregion
21.  
22.         #region stepC
23.         if (GUILayout.Button("Load P", GUILayout.Width(200), GUILayout.Height(150))) {
24.             if (assetBundleP == null) {
25.                 Debug.LogError("Load AB_P Failed, Forgot?");
26.             } else {
27.                 GameObject asset = assetBundleP.LoadAsset<GameObject>("Assets/Prefab/PlayableDirector.prefab");
28.                 var pd = asset.GetComponent<PlayableDirector>();
29.                 Debug.Log(pd.name);
30.             }
31.         }
32.         #endregion
33.  
34.         #region stepD
35.         if (GUILayout.Button("Load T", GUILayout.Width(200), GUILayout.Height(150))) {
36.             if (assetBundleT == null) {
37.                 Debug.LogError("Load AB_T Failed, Forgot?");
38.             } else {
39.                 var asset = assetBundleT.LoadAsset<TimelineAsset>("Assets/Prefab/TestTimeline.playable");
40.                 Debug.Log("asset.outputTrackCount = " + asset.outputTrackCount);
41.             }
42.         }
43.         #endregion
44.  
45.     }
46. }

a -> b -> d -> c : asset.outputTrackCount == 4
a -> b -> c -> d : asset.outputTrackCount == 0

Mabe there is a bug here.

Here is the test package.