Why does the xaml display wrong, even after changing and saving?

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C#

XAML

Android

Xamarin

In a Grid layout:
R1c4ImageButton should be diamond but nothing appears,
R2c2ImageButton should be octagon but nothing appears,
R2c3ImageButton should be oval but octagon appears,
R2c4ImageButton should be pentagon but oval appears.

All of the Source names are valid images and work if I change during Debug with Hot Load and in the C# coding.
All of the ImageButtons are valid and work with Source changes during Debug with Hot Load and in C# coding.

The XAML code is:

<ImageButton x:Name="R1c1ImageButton"
 Grid.Column="0"
 Grid.Row="0"
 Source="arrow"
 Clicked="R1c1ImageButton_Clicked">
<ImageButton x:Name="R1c2ImageButton" 
 Grid.Column="1"
 Grid.Row="0"
 Source="circle"
 Clicked="R1c2ImageButton_Clicked">
<ImageButton x:Name="R1c3ImageButton" 
 Grid.Column="2"
 Grid.Row="0"
 Source="cross"
 Clicked="R1c3ImageButton_Clicked">
<ImageButton x:Name="R1c4ImageButton" 
 Grid.Column="3"
 Grid.Row="0"
 Source="diamond"
 Clicked="R1c4ImageButton_Clicked">
<ImageButton x:Name="R2c1ImageButton" 
 Grid.Column="0"
 Grid.Row="1"
 Source="hexagon"
 Clicked="R2c1ImageButton_Clicked">
<ImageButton x:Name="R2c2ImageButton" 
 Grid.Column="1"
 Grid.Row="1"
 Source="octagon"
 Clicked="R2c2ImageButton_Clicked">
<ImageButton x:Name="R2c3ImageButton" 
 Grid.Column="2"
 Grid.Row="1"
 Source="oval"
 Clicked="R2c3ImageButton_Clicked">:
<ImageButton x:Name="R2c4ImageButton" 
 Grid.Column="3"
 Grid.Row="1"
 Source="pentagon"
 Clicked="R2c4ImageButton_Clicked">

What I have tried:

If I retype the Source name in Debug, Hot Load will change the image.
If I then Save and close the solution and reopen I get the same erroneous display.

I have closed and reopened Visual Study, Solution, and even created release and installed on a separate tablet and still see the same display.