Unexpected "Unnecessary using directive." diagnostics is reported

[AlekseyTs]

Using this VB assembly as a reference

Public Class C1
    Public Shared Property P1(x As Integer)
        Get
            Return Nothing
        End Get
        Set
        End Set
    End Property
End Class

compile this C# code

using static C1;

public class C2
{
    public static void Main()
    {
        P1[0] = null;
    }
}

Observed:

// (2,1): hidden CS8019: Unnecessary using directive.
// using static C1;
Diagnostic(ErrorCode.HDN_UnusedUsingDirective, "using static C1;").WithLocation(2, 1),
// (8,9): error CS1545: Property, indexer, or event 'C1.P1[int]' is not supported by the language; try directly calling accessor methods 'C1.get_P1(int)' or 'C1.set_P1(int, object)'
//         P1[0] = null;
Diagnostic(ErrorCode.ERR_BindToBogusProp2, "P1").WithArguments("C1.P1[int]", "C1.get_P1(int)", "C1.set_P1(int, object)").WithLocation(8, 9)

Expected: No CS8019 diagnostics, if there were no that using directive, P1 wouldn't be found.