Designer: deleting a TabPanel tab leaves its hosted controls orphaned

Deleting a tab from a TabPanel in the visual designer leaves any controls hosted on that tab in the layout. They disappear from the design surface and can no longer be selected there, but they remain in the project file and still appear in the hierarchy view under the deleted tab. Deleting a tab should remove the controls hosted on it (including nested descendants), move controls on later tabs down so they stay on the same logical tab, and be undoable as a single action.