The tab label is of the form ‘view-type: view’s root container’. At very start, the view root will be the root of the document, this the TBX’s name minus the TBX extension. Changing the note selected in a view (i.e. the text pane contents) does not - as your post would imply- alter the tab label, it only alters the title in the text pane.
But if you drill down into a map container (or hoist a child in outline, etc.) the root of the view has changed and that container name now forms the second part of the tab label.
To avoid the tab label changing, don’t change it’s root view.