Wpf rendering inconsistent when used with material design - wpf

Question

I have following XAML in my WPF Control:
App.Xaml
<Application x:Class="MyWPFApp"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:miscellaneous="clr-namespace:MyWPFApp.Miscellaneous"
Startup="OnAppStart">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<materialDesign:CustomColorTheme BaseTheme="Light" PrimaryColor="#FF0080FF" SecondaryColor="White" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/materialdesigntheme.Flipper.xaml" />
<ResourceDictionary Source="Converters/Converters.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
This renders the text box without validation error below, when I run the application and type something in the text box:
XAML 1
<Grid>
<TextBox
Style="{StaticResource MaterialDesignFloatingHintTextBox}"
VerticalAlignment="Center"
md:TextFieldAssist.HasClearButton="True"
md:HintAssist.Hint="Email Address"
md:HintAssist.HelperText="{Binding ErrorContent}">
<TextBox.Text>
<Binding
UpdateSourceTrigger="PropertyChanged"
ValidatesOnNotifyDataErrors="True">
<Binding.Path>Email</Binding.Path>
</Binding>
</TextBox.Text>
</TextBox>
</Grid>
But when I changed the XAML as follows (Grid enclosed in a MaterialDesign.DialogHost element):
XAML 2
<md:DialogHost>
<Grid>
<TextBox
Style="{StaticResource MaterialDesignFloatingHintTextBox}"
VerticalAlignment="Center"
md:TextFieldAssist.HasClearButton="True"
md:HintAssist.Hint="Email Address"
md:HintAssist.HelperText="{Binding ErrorContent}">
<TextBox.Text>
<Binding
UpdateSourceTrigger="PropertyChanged"
ValidatesOnNotifyDataErrors="True">
<Binding.Path>Email</Binding.Path>
</Binding>
</TextBox.Text>
</TextBox>
</Grid>
</md:DialogHost>
The rendering is exactly what I was expecting:
My question is, shouldn't be the rendering like in Figure. 2 with XAML 1?

Answer 1

Yes, it should provided that there is an AdornerDecorator somewhere above the Grid in the element tree.
Putting your sample markup in a default Window works just fine, i.e. the error message is display as expected.
This is all there is in App.xaml:
<Application x:Class="WpfApp1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<materialDesign:BundledTheme BaseTheme="Dark" PrimaryColor="DeepPurple" SecondaryColor="Lime" />
<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
Using MaterialDesignThemes 3.1.3.