Asynchronous Child Actions Still not Supported in .NET 4.5.1

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We have updated our project to .NET 4.5.1, but we see asynchronous child actions still not supported: When we tried to use ChildAction, we got the following error message:

Server Error in '/' Application.

HttpServerUtility.Execute blocked while waiting for an asynchronous operation to complete.  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

__ __
Exception Details: System.InvalidOperationException: HttpServerUtility.Execute blocked while waiting for an asynchronous operation to complete.

Source Error:
…
 

The sample:

Controller:

public class HomeController : Controller 
{ 
    public ActionResult Index() 
    { 
        return View(); 
    }

    [ChildActionOnly] 
    public async Task<ActionResult> ChildV() 
    { 
        await Task.Delay(2000); 
        return Content("ChildView"); 
    } 
}

ChildView:

@{ 
ViewBag.Title = "Index"; 
} 
<h2>Index</h2> 
@Html.Action("ChildV")

Please read more detail from here.