DatePicker with Floating Hint Style's Top Margin/Padding mismatch from TextBox Style

[HClausing]

The elements are inside a StackPanel, on "Form" GroupBox. The two images below show the distance from top element and its flow Label (Hint):

DatePicker:

XAML:

    <GroupBox Header="Form:" Margin="15,15,15,15" 
              materialDesign:ColorZoneAssist.Mode="Standard"
              Style="{StaticResource MaterialDesignCardGroupBox}"
              materialDesign:ShadowAssist.ShadowDepth="Depth0"
              Grid.Column="1" DataContext="{Binding ElementName=dgmain, Path=SelectedItem, ValidatesOnNotifyDataErrors=False}">

        <StackPanel>
            <TextBox Style="{StaticResource MaterialDesignFloatingHintTextBox}" 
                     materialDesign:HintAssist.Hint="Título"  Margin="5,0"
                     Text="{Binding Title, ValidatesOnNotifyDataErrors=False}"/>

            <TextBox Style="{StaticResource MaterialDesignFloatingHintTextBox}" 
                     materialDesign:HintAssist.Hint="Autor"  Margin="5,0" 
                     Text="{Binding AuthorFullName, ValidatesOnNotifyDataErrors=False}"/>
            
            <DatePicker Style="{StaticResource MaterialDesignFloatingHintDatePicker}"
                        materialDesign:HintAssist.Hint="Publicado em"  Margin="5,0" 
                        SelectedDate="{Binding PostDate, TargetNullValue='', ValidatesOnNotifyDataErrors=False}"/>

            <TextBlock Text="Teste..." Margin="15" />
        </StackPanel>
    </GroupBox>