A. Here is the scenario, that works OK via the browser:
--you select a specific notebook, on the left column.
--you type in multiple words in the search box, and the search is done.
--you then need to change and redo the search, so you triple-click in the search box, which selects all the words, and you enter a new search, which is done fine, within the selected notebook.
B. Unfortunately, this does not work the same way on the Mac implementation:
--when you select a notebook, it is inserted at the front of the search box.
--you can type multiple words and do a search.
--but if you want to re-edit the search, you triple-click on the text, which selects all the words AND THE NOTEBOOK SELECTION.
--when you type a new search it replaces the old text AND THE NOTEBOOK SELECTION, so the revised search is performed across all notebooks, not in the notebook you selected.
C. Possible change: have triple-click in the search box only select the text, and not also select the notebook specification. If you need to change notebooks, explicitly delete notebook selection.