Derived Pages generate incorrect code.

I'm trying to derive all may pages from a base class in my Visual Studio Xamarin Forms project, but it generates incorrect code that when compiled gives the follow error:

error CS0234: The type or namespace name 'local' does not exist in the namespace 'Xamarin.Forms' (are you missing an assembly reference?)

Its easily reproducible by the following steps:

1. Create a Visual Studio project, 'Blank Xaml App', called AppTest.
2. Add a new item (Forms Xaml Page) to the project, called BasePage.

3. Derive the existing MainPage.xaml from BasePage
   

   <?xml version="1.0" encoding="utf-8" ?>
   <local.BasePage
       xmlns="http://xamarin.com/schemas/2014/forms"
       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
       xmlns:local="clr-namespace:AppTest;assembly=Apptest"
       x:Class="local.MainPage">
       <Label Text="Welcome to Xamarin Forms!" VerticalOptions="Center"   HorizontalOptions="Center" />
   </local.BasePage>

4. Derive the existing MainPage.xaml.cs from BasePage
   public partial class MainPage : BasePage

Building the project generates the code:

public partial class MainPage : global::Xamarin.Forms.local.BasePage {

and gives the above CS0234 compile error.

Manually changing the generated code to:

public partial class MainPage : BasePage {

solved the issue, but isn't (for many reasons) a solution.

What am I doing wrong?
Doesn't anyone know how to make it generate the correct code?

Environment:
Visual Studio Pro 2015
Xamarin Forms 2.3.3.180
Microsoft.NETCore.UniversalWindowsPlatform 5.2.2

Any help is much appreciated.