Won't 'IsHidden' make the unpinned window completely disappear? We still want the window to be available when the modal dialog is closed.
In your test, make sure you don't select the unpinned window (by clicking on its titlebar for example). If you select it with the mouse, the problem doesn't occur. We make the unpinned window appear in code when it's required:
view.DockingPanel.ActivePane = pane;
pane.IsSelected = true;
Next, do a ShowDialog on a new rad window
I see this behavior (attached)