And yet it's bewilderingly common to use it as a low-pass filter. The reason I like the suggestion is that it asks the candidate to show you how something work

And yet it's bewilderingly common to use it as a low-pass filter. The reason I like the suggestion is that it asks the candidate to show you how something works which seems like it would demonstrate their ability to understand a topic, how they approach it, and importantly whether they can communicate what they know in a way that other people can understand. I'm more interested in whether a candidate can write a decent bug report and form a coherent patch than how many puzzle solutions they've memorized to slip through my filters.