WebForms: R# does not recognise async model binding

Async model binding was added to WebForms in .NET 4.6 back in 2015:

Cool ASP.NET Web Forms Features in 2015 – Async Model Binding | ASP.NET Blog

R# 2018.1 still doesn't recognise it, and flags it as an error: Parameters do not match to the method signature

<asp:GridView runat="server" SelectMethod="LoadData">

public async Task<IEnumerable<SomeClass>> LoadData() => ...

The project is targeting .NET 4.6; the latest Roslyn compilers are installed and configured; and the project C# language level is set to "C# 6.0".

The code compiles and runs perfectly.

JetBrains ReSharper Ultimate 2018.1  Build 112.0.20180414.70444
ReSharper 2018.1.20180414.71556
VisualStudio.15.Release/15.7.1+27703.2000
Microsoft .NET Framework Version 4.7.03056
Windows 10 Pro 64-bit v1803 (build 17134.48)