The pane that wouldn’t go away

• A pane left holding a tab that was closed somewhere else used to sit in the window as a blank column — nothing in it, no way to close it, shrink it or click into it, and the only way out was resetting your whole layout. Now it tells you the tab is gone and gives you a button to close the pane, and a pane with nothing left to show stops taking up room in the window.