Search box sometimes deletes part of what the user types and goes to the wrong page (T53900)

In certain specific cases (when typing more text after selecting a search suggestion; see the bug report for details) the search suggestions code causes some of the inputted text to be ignored, searching for the wrong thing. Fix this! :)

The issue affects the jquery.suggestions and mediawiki.searchSuggest modules.

Please read the complete bug description and comments on the bug report (T53900), as they are often very helpful. Students are required to read Wikimedia's general instructions first.