Workaround for asset reference problem.

MakeState1-2

@MenuItem ("MyMenu/Do Something")

static function DoSomething () {
	var header1 = ScriptableObject.CreateInstance.<StateHeader>();
	var header2 = ScriptableObject.CreateInstance.<StateHeader>();

	AssetDatabase.CreateAsset(header1, "Assets/State1Set.asset");
	AssetDatabase.CreateAsset(header2, "Assets/State2Set.asset");

	var state1 = ScriptableObject.CreateInstance.<State1>();
	var state2 = ScriptableObject.CreateInstance.<State2>();

	state1.reference = state2;
	state2.reference = state1;
	
	AssetDatabase.AddObjectToAsset(state1, header1);
	AssetDatabase.AddObjectToAsset(state2, header2);

	AssetDatabase.ImportAsset(AssetDatabase.GetAssetPath(state1));
	AssetDatabase.ImportAsset(AssetDatabase.GetAssetPath(state2));
}