In a WPF application I defined default control styles in separate resource dictionaries (e.g. "ButtonStyle.xaml"), and added them as merged dictionaries to a resource dictionary named "ResDictionary.xaml".

If I refer this "ResDictionary.xaml" as merged dictionary in my App.xaml, the default styles are not applied. However, if I refer the "ButtonStyle.xaml", it works correctly.

If I recompile the same code in .NET 3.5 or 3.0, it recognizes and applies the default styles referred in "App.xaml" through "ResDictionary.xaml", but not in .NET 4.0.

At runtime if I check the Application.Current.Resources dictionary, the default styles are there, but they are not applied, only if I specify the Style property explicitly in the Button control.

Are there any solutions to refer a resource dictionary (containig default styles) this way in .NET 4.0?

App.xaml:

<Application.Resources>
  <ResourceDictionary>
    <ResourceDictionary.MergedDictionaries>
      <ResourceDictionary Source="Styles/ResDictionary.xaml"/>
    </ResourceDictionary.MergedDictionaries>
  </ResourceDictionary>
</Application.Resources>

ResDictionary.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="Default/ButtonStyle.xaml"/>
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

ButtonStyle.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Style TargetType="Button">
        <Setter Property="Background" Value="Yellow"/>
    </Style>
</ResourceDictionary>