What web browser are you using? Option arrow works right for DDG's location bar on safari + firefox, and duckduckgo.com and google.com's search bar's option arrow works properly under safari.
If you are in the pull down of search suggestions and in the search field is standing (copied) the suggestion where you currently are, then when you hit arrow, the search field jumps back to your search string. It should instead led you edit the selected suggestion.
