Adding a resource to WPF application causes build error

I'm working through the book Head First C# and consistently have issues when adding resources to a window. This is a 100% repeatable error on any new WPF application I create when adding a new resource. The only way around this is to comment out the resource, build, and uncomment, as detailed in MVCE below. Images are included as proof this isn't a what-if or theoretical scenario.

What are the proper steps to add a resource file and use it within a WPF project?

I'm using Visual Studio Community 2017: Version 15.9.9 Target framework: .NET Framework 4.6.1

MVCE:

1. Create a new WPF application. Add a class:

   //MyDataClass.cs
   using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Text;
   using System.Threading.Tasks;
   
   namespace XAMLBuildErrorExample
   {
       class MyDataClass
       {
           public string Foo { get; set; }
       }
   }
   

2. Within MainWindow.xaml add a resource

   <Window x:Class="XAMLBuildErrorExample.MainWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
           xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
           xmlns:local="clr-namespace:XAMLBuildErrorExample"
           mc:Ignorable="d"
           Title="MainWindow" Height="450" Width="800">
       <Window.Resources>
           <local:MyDataClass x:Key="exampleResource" />
       </Window.Resources>
   
       <Grid>
   
       </Grid>
   </Window>
   

3. Attempt to build. Error "The tag 'MyDataClass' does not exist in XML namespace 'clr-namespace:XAMLBuildErrorExample'. Line 11 Position 10.":

   

4. Comment out the resource. Build succeeds:

   

5. Uncomment resource. Build succeeds whereas it failed before:

   

6. Any subsequent cleaning of the solution makes building impossible because of the error in the first image.