I thought you were joking but it's true. Try removing all characters here: https://hn.algolia.com/?query=china&sort=byPopularity&prefix... and type out "china", look at the bottom results and then press "Enter", now you get different stories.
What awful UX, what was the thinking behind that? People who search for the same thing gets different results, depending on if they actually searched or if they just typed it out.
Search-as-you-type is much more a guide during the search, it shows you a preview of possible results from what you've currently typed both as a whole query and as the beginning of a query.
All other variation are worth: no prefix during search as you type means that you'll have an empty result most of the time or things that are completely irrelevant; keeping prefix on the final search means that you'll see a lot of irrelevant results (especially with typo-tolerance).