Yesterday I searched for an article I read 2 or 3 days ago (this one: https://news.ycombinator.com/item?id=30007856). I was 70% sure that the words "home" and "network" appeared in the post, so I searched in "Stories" in "Past Week" for these keywords and didn't find it.
I had to switch to "All" and noticed that the search engine didn't take the word "networking" into account which appeared in the title. I would argue that stemming and searching for root words is a basic feature of a modern search engine, if I type "site:news.ycombinator.com home network" into Google, I find the article without any problems.
So to sum up: What is the intention behind the way the search engine works? If I would type in "home network" in a full-text search engine, even that would give me the correct article but for some reason HN's search engine is not capable of that.
Is it not the case for you?
guess it's simply just rather good SE not on the top class (google, amazon, yandex, bing etc)