Problem when splitting app.xaml into several files

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C#

XAML

WPF

I try to split app.xaml into several xaml-files. It seems to work for most things, but not for things reffering to clr-namespace. I started out by moving "everything" from app.xaml to another file. I'll try to explain with a small example.

App.xaml

<Application x:Class="Preparation.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:src="clr-namespace:Preparation.DataModel" 
             xmlns:conv="clr-namespace:Preparation.Converters"
             xmlns:viewmodel="clr-namespace:Preparation.ViewModel"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="AppRevision.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>

    </Application.Resources>
</Application>

AppRevision.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:src="clr-namespace:Preparation.DataModel" 
             xmlns:conv="clr-namespace:Preparation.Converters"
             xmlns:viewmodel="clr-namespace:Preparation.ViewModel"
>

    <!-- <conv:DateConverter x:Key="dateConverter"/>
    <conv:IntToStringConverter x:Key="IntToOvenSeqMode" FalseValue="Hold"   TrueValue="Ramp" />-->

    <Style x:Key="titleStyle" TargetType="TextBlock">
        <Setter Property="FontWeight" Value="Bold"/>
        <Setter Property="Foreground" Value="DodgerBlue"/>
        <Setter Property="FontSize" Value="18"/>
    </Style>

    <DataTemplate DataType="{x:Type src:TableHandler}">
     ...
    </DataTemplate>
</ResourceDictionary> 

I can compile the project, but when starting it I get the following message at the DataType:

System.Windows.Markup.XamlParseException
InnerException: {"Type reference can't find any type with name {clr-namespace:Preparation.DataModel}TableHandler."}

If i don't comment out the DateConverter, I get a similar error there instead.

The odd thing is that it works when the code is inside app.xaml.
I guess that it's a simple error, but I haven't been able to find it.