Async / Await in WebForms - How does the continuation continue until the page life cycle?

I tested async in WebForms, and this time my question is not how to do something, but how does something that works. This is my test code:

protected override void OnPreRender(EventArgs e)
{
    Response.Write("OnPreRender<Br>");
}
protected override void OnPreRenderComplete(EventArgs e)
{
    Response.Write("OnPreRenderComplete<Br>");
}
protected async override void OnLoadComplete(EventArgs e)
{
    Response.Write("OnLoadComplete<br>");
    var t1 = Task.Factory.StartNew(() => {
        System.Threading.Thread.Sleep(2000);
        return 1;
    });

    //This actually does run:
    Response.Write((await t1).ToString());
}

So my task pauses a bit and then writes the result. My question is: I would not expect this to work because the control was obtained from the OnLoadComplete method - I would expect the page to actually finish rendering and be returned to the client before my task ever returns.

Actual conclusion:

OnLoadComplete
OnPreRender
1OnPreRenderComplete

, , OnLoadComplete , OnPreRender , OnLoadComplete. , "1" , , , . , , , 10 , .

, WebForm - , . - , ? async/wait , , , , , .