The diagram does not know what graphics elements are drawn inside hosted controls to export them. Try using CompositeNode objects instead; we've created them as light-weight alternative of ControlNode, they work better both for exporting and user interaction (e.g. hit-testing is not stopped by hosted controls, and CompositeNodes can appear behind other items in Z order). If you prefer ControlNodes, you will have to handle the DiagramView.PaintControl event to render your own representation of their contents in exported documents.

I hope  that helps,
Stoyan