Asynchronously Load a Scene, then switch to it on function call Unity 5.3

I made a game back before Unity 5.3 that used Application.LoadLevelAsync, which is now deprecated. I am trying to achieve the same result: on a startup menu, load a scene asynchronously in the background, and then switch to it on a button press. I’ve tried SceneManager.LoadSceneAsync("level1", LoadSceneMode.Single);, but it just switches to the scene once it’s done loading. It doesn’t seem to behave any differently than SceneManager.LoadScene().

My code that runs SceneManager.SetActiveScene(SceneManager.GetSceneByName("level1")); is never called, so I’m not sure why it’s switching to the level1 scene once it’s done asynchronously loading.

Any ideas?

Edit: It does not work in both the editor and a standalone web player or built for Windows.

var operation = SceneManager.LoadSceneAsync(“level1”, LoadSceneMode.Single);
operation.allowSceneActivation = false;
This should stop the Scene from being activated right away.