OneNote Interop API targets wrong window instance

You are invoking the add-in from the second OneNote window, but the application-level Interop calls behave as though the first window owns the current page until the second window is edited. Microsoft exposes open windows through Application.Windows: CurrentWindow identifies the active Window, and each Window provides Active and CurrentPageId. Capture Windows.CurrentWindow at command start, verify that Active is true, and store its CurrentPageId before making a content call. Enumerate the Windows collection to confirm which instance OneNote reports as active. UpdatePageContent targets content by page ID; it does not target a UI window. When two windows show the same page, the API offers no separate window-specific update target. After the update, reactivate the captured Window and verify its CurrentPageId. If OneNote still refreshes only the first window, provide a minimal two-window reproduction and build number to Microsoft. The documentation does not guarantee that UpdatePageContent refreshes the invoking window.