orleans: Using named C# 7 ValueTuples in grain interfaces results in a compilation error

Using a named C# 7 ValueTuple in the definition of a grain interface results in a compilation error.

This:

public interface ISomeGrain : IGrainWithIntegerKey
{
    Task<(bool someBool, string someString)> Func();
}

results in this error in the generated .Orleans.g.cs file:

CS8141	The tuple element names in the signature of method must match the tuple element names of interface method (including on the return type).

The same does not happen if the tuple is unnamed.