Edit XAML Brushes in Design mode by Stoffis1

Tried the new Blend 5 Update 2 CTP 2 for VS 2012.
Now, I have a simple XAML Brush, in a Resource Dictionary, and tried to click on the xaml file, but no, it is not able to preview it in Design mode.
I can see a small image on the right hand side on the tab Resources (so It is possible for Blend to preview the brush correctly) so Why can´t I see this in the big Preview page?
(I can only edit the xaml code, and this can be done in VS 2012 anyways)
I need also a way to edit the paths, so I can edit my xaml brushes (images) correctly in a grapgical manner...

You can download a sample of such a brush from here: www.xamalot.com
and select Brush and all checkboxes checked...