Long titles cannot be removed from recent searches because the “x” button overlaps the titles making it re-enter the titles in the search area instead of removing them.
1920x1080.
Since your screen is bigger than mine try searching for a show with even bigger title so much so that the title text goes under that “x” button.
Then even you won’t be able to remove the search.
Oh, that’s odd, mine is also 1920x1080.
Anyway, I’ve tagged the developer about this.
Thanks for reporting!