Why does binding affect height?

Style definition in Resources/Shared.xaml (updated):

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:system="clr-namespace:System;assembly=mscorlib">
<system:Double x:Key="fullHeight" >26</system:Double>
<system:Double x:Key="halfHeight" >16</system:Double>
<Thickness x:Key="m">10</Thickness>
<Style TargetType="Button">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
    <Setter Property="Padding" Value="10"/>
</Style>
<Style TargetType="Label">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
    <Setter Property="VerticalAlignment" Value="Center"/>
</Style>
<Style TargetType="TextBlock">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
</Style>
<Style TargetType="TextBox">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
    <Setter Property="Padding" Value="10"/>
</Style>
<Style TargetType="PasswordBox">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
    <Setter Property="Padding" Value="10"/>
</Style>
<Style TargetType="ListView">
    <Setter Property="FontSize" Value="{StaticResource fullHeight}"/>
    <Setter Property="Margin" Value="{StaticResource m}"/>
    <Setter Property="Padding" Value="10"/>
</Style>
<Style TargetType="ComboBox">
    <Setter Property="Margin" Value="{StaticResource m}"/>
</Style>
</ResourceDictionary>

Window:

<Window.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="../Resources/Shared.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Window.Resources>

User control:

<StackPanel Orientation="Horizontal">
  <Label Content="Text" Background="AliceBlue"/>
  <Label Content="{Binding DecimalValue, FallbackValue=50}" Background="Aquamarine"/>
</StackPanel>

Model:

    private decimal _DecimalValue;
    public decimal DecimalValue
    {
        get { return _DecimalValue; }
        set
        {
            if (_DecimalValue != value)
            {
                _DecimalValue = value;
                NotifyOfPropertyChange();
            }
        }
    }

I'm using Caliburn.Micro if it makes any difference.

Result:

enter image description here

Why?

Update: After some Snooping, it turns out that the inner TextBlock of the first Label has margin of 0 and Value Source is Default and for the second it's 10 and Style.

Update 2: After reading up this question it turns out that defined TextBlock style should not be applied to TextBlocks inside Labels. So it seems that existence of binding on a Label somehow changes that.

You must have some other style affecting it.

My best guess would be check your Padding properties, because when I copy and paste your styles to a new project, the heights and margins are the same as your image, however the Padding is different.

Your Labels are actually getting rendered like this:

<Label>
    <Border>
        <ContentPresenter>
            <TextBlock />
        </ContentPresenter>
    </Border>
</Label>

By messing around with Snoop, I can duplicate your image by altering the Padding of the Border object, so check your XAML to see if you have any implicit styles that change the Padding of your Border tags

Update

After adding the extra styles you've added to your question, I am able to reproduce the results you are getting.

The problem appears to be that the implicit style for your TextBlock is being applied to the TextBlock inside the bound label, but not to the unbound one.

It should be noted this only happens when binding to a decimal value, not to a string.

I suspect this is related to the fact that implicit styles are not meant to cross template boundaries, unless the element inherits from Control. Label inherits from Control, however TextBlock does not.

Since this only happens when binding to a numeric value, my best guess is that the process that determines how to draw a Decimal for Label.Content identifies the parent control as a Label, while the process that writes a string to Label.Content automatically knows to use a TextBlock, and does not apply the implicit styles.

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