wpf xaml designer bug

every time we open a *.xaml file in our project - we see not working designer and a lot of messages 'type not found' 'assembly not found' etc. After a couple of experiments, i found out a root of a problem : create new WPF application, create a folder in project root, add some value converter to folder, try to use it on your 'MainWindow.xaml'

you will probably write something like this :

xmlns:Folder="clr-namespace:WpfApp.Folder"

and then

   <Window.Resources>
        <Folder:SomeValueConverter x:Key="someKey"/>
    </Window.Resources>

You know...

And, now the most interesting thing! when you build your project for x86 or 'any CPU' - everything will be just fine, designer will be available, all namespaces will be imported perfectly!BUT, just change you project configuration to x64...Rebuild solution and open design view... You'll be amazed...errors, types not found, etc... How the hell to use VS xaml designer in x64 applications?

Windows 7 enterprise x64, Visual Studio 2010 Ultimate