Blend does not call DesignTimeBootstrapper

I need Blend 4 to call some initialization code before it can display my application, and I use this Josh Smith approach to get it done.

I use the following project structure:

MainProgram
  -- Properties
     -- AssemblyInfo.cs (including the custom attribute)
  -- App.xaml
  -- HostWindow.xaml    (UserControls are embedded here)
  -- DesignTimeBootstrapperAttribute.cs

ViewsAssembly
  -- Lots of user controls

For some reason, the development-time bootloader is not called after each build (which leads to the creation of custom markup extensions that throw exceptions and a lot of error messages in Blend). However, it gets called when the solution is first loaded, and I don’t understand how Blend behaves here.

What am I doing wrong, or is there a different approach?

Edit: , Bootstrapper . , , .