is this a bug?

Unity Engine
1

1.BuildPipeline AAA to aaa.unity3d (AAA is a prefab which use MecanimSystem.)
2.WWW down aaa
3.obj = Instantitate www.assetbundle.mainAsset //ALL IS OK. animator work well
4.www.assetbundle.Unload(false); //ALL IS OK. animator work well
5.Resources.UnloadUnusedAssets();
//if AAA’s AnimationType is Humanoid ,then obj’s animator don’t work.no animation!
//if AAA’'s AnimationType is Generic,then the editor is crash. And the Edtior.log : “Dereferencing null pttr.”

2

Probably yes, please report it via “Help > Report a bug” attaching project or at least asset bundle you used and post case number here