(Option to) make an aborted search request permanent and prevent it from loading in the background
Sometimes you hit the search button to early by mistake, starting a request that takes quite a long time to load. If you cancel this request and make a new request, the new one will often be completed earlier, giving you the right results. Yet the original request would continue to load in the background, making the results list to switch back to the wrong results.
For example you are searching for "appendix" but hit enter after typing "a". Now you can cancel this request while it is loading, and do the right one for "appendix". Some time after you got the results for "appendix" yet the results would switch back to the results for "a" a few seconds later as that reuest was still executed in the background.

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Stacey van Groll commented
I agree that this is problematic behaviour. I haven't reported it but in hindsight think I should have given it seems a defect rather than desired intention design. I can't think of any reason why a user cancelling a search , the user continuing in UI to other activities, and then those other activities being disrupted by the search completing regardless would be deliberate. Cancel needs to mean cancel.