Creative professions usually are like this. Also (more anecdotally) I find that quite a few researchers like doing some research during their free time (usually

Creative professions usually are like this. Also (more anecdotally) I find that quite a few researchers like doing some research during their free time (usually far less serious research of the form "applying techniques used in research on toy problems"). It's not uncommon, but then again, not all programmers spend their free time on more programming.