WPF button content (vector drawing) not visible - wpf

Question

I have in resource dictionary Buttons.xml two vector drawings for to be shown as a button content.
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Viewbox
x:Key="BlueMinusButton"
Height="20"
Stretch="Uniform">
<Canvas
Width="100"
Height="100">
<Canvas.LayoutTransform>
<ScaleTransform
ScaleX="1"
ScaleY="-1"
CenterX=".5"
CenterY=".5" />
</Canvas.LayoutTransform>
<Ellipse
Canvas.Left="0"
Canvas.Top="0"
Height="100"
Width="100"
Fill="Blue" />
<Line
X1="10"
X2="90"
Y1="50"
Y2="50"
Fill="Black"
StrokeThickness="10"
Stroke="Black" />
</Canvas>
</Viewbox>
<Viewbox
x:Key="GreenPlusButton"
Height="20"
Stretch="Uniform">
<Canvas
Width="100"
Height="100">
<Canvas.LayoutTransform>
<ScaleTransform
ScaleX="1"
ScaleY="-1"
CenterX=".5"
CenterY=".5" />
</Canvas.LayoutTransform>
<Ellipse
Canvas.Left="0"
Canvas.Top="0"
Height="100"
Width="100"
Fill="Green" />
<Line
X1="10"
X2="90"
Y1="50"
Y2="50"
Fill="Black"
StrokeThickness="10"
Stroke="Black" />
<Line
X1="50"
X2="50"
Y1="10"
Y2="90"
Fill="Black"
StrokeThickness="10"
Stroke="Black" />
</Canvas>
</Viewbox>
</ResourceDictionary>
In view1.xaml I have three buttons and other controls and I use from resources same content for two buttons.
<UserControl
x:Class="ApplicationName.View1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:ApplicationName">
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary
Source="Buttons.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition
Height="Auto" />
<RowDefinition
Height="Auto" />
<RowDefinition
Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition
Width="*" />
<ColumnDefinition
Width="Auto" />
</Grid.ColumnDefinitions>
<Label
Grid.Column="0"
Grid.Row="0"
Content="Object1" />
<Button
Grid.Column="1"
Grid.Row="0"
Content="{StaticResource BlueMinusButton}"
Command="{Binding DoCommand1}" />
<Label
Grid.Column="0"
Grid.Row="1"
Content="Object2" />
<Button
Grid.Column="1"
Grid.Row="1"
Content="{StaticResource GreenPlusButton}"
Command="{Binding DoCommand2}" />
<Label
Grid.Column="0"
Grid.Row="2"
Content="Object3" />
<Button
Grid.Column="1"
Grid.Row="2"
Content="{StaticResource GreenPlusButton}"
Command="{Binding DoCommand3}" />
</Grid>
</UserControl>
view1.xaml is used in view2.xaml.
<UserControl
x:Class="ApplicationName.View2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="ApplicationName">
<Grid>
<StackPanel>
<Label
Content="Controls" />
<local:View1
DataContext="{Binding View1Context}"/>
<Label
Content="Other controls" />
</StackPanel>
</Grid>
</UserControl>
Here comes the problem: When looking the view2.xaml in xaml editor, the content for the middle button is missing. Same happens in run time. If I look view1.xaml in xaml editor, all the button contents are visible. Here is a picture from the views:
Why the content is not shown and how do I get it back?

Answer 1

Set x:Shared="False" for your each ViewBoxif you want to useit in multiple places.