Insertion of new document placement

I am switching to the new Docking framework and when I insert a new document it alwasy adds it at he beginning and shifts all the other ones to the right. This can be seen also in the MVVM DocumentWindows sample. How do I insert the document as the last tab in order to prevent that shifting motion? I tried to use the Flowdirection property but then eveything is shifted the right.

Any help is appreciated.

Thanks.