To reproduce:
Use the BugTracker project from the {IntallationFolder}\Examples\BugTracker
1. Change the CloseAction for all DocumentWindows to "Hide".
2. Run the application.
3. Close tab "Bugs"
4. Save the layout, pressing the "Save" button ribbon tab "view"
5. Load the layout.
 You will notice that the "Bugs" tab is visible but in a invalid state.

Workaround: use  DocumentWindow.CloseAction = Close or call  DocumentWindow.Show method before loading the layout.