WPF not applying default styles defined in MergedDictionaries?

The best solution is to add a dummy default style in the resource dictionary where you merge all resources together.

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"><ResourceDictionary.MergedDictionaries>    <ResourceDictionary Source="Style/Button.xaml"/></ResourceDictionary.MergedDictionaries><Style TargetType="Control" BasedOn="{StaticResource {x:Type Control}}" />

This could be caused by a known bug when there is a single style in application.resources within app.xaml when not using a startupuri.

The fix is to add an additional style like this...

...   <Style x:Key="unused" /></Application.Resources>

for more details check out this link.... http://bengribaudo.com/blog/2010/08/19/106/bug-single-application-resources-entry-ignored

There is a sort-of fix for this, but I’ve only been able to make it work at the window level (not the application level).

In order to include a WPF 4.0 resource from a separate project, the resource must be added as a resource in the window’s code behind. The statement belongs in the window’s constructor, prior to the InitializeComponent method call:

public ControlsWindow(){    this.Resources = Application.LoadComponent(new Uri("[WPF 4.0 ResourceProjectName];Component/[Directory and File Name within project]", UriKind.Relative)) as ResourceDictionary;    InitializeComponent();}

Note: Replace the '[WPF 4.0 ResourceProjectName]' text with your resource's project name. Also, the '[Directory and File Name within project]' needs to be replaced with the relative location of the resource file (like 'Themes/StandardTheme.xaml')

I go into more details about this issue here.