Mods of any decently sized forum can point to very special users participating in intense sockpuppetry, flamewars, getting back after being banned 20 times, and so on. It's not specific to 4chan.
It's also somewhat expected on the site from a cultural standpoint? Having a recognizable posting pattern gives flavor to a system that is otherwise composed of completely interchangeable posters. Like /v/ has one guy that constantly makes threads that are designed to devolve as quickly as possible into posting images of anthropomorphic lizards. It's not much of a nuisance so much as it makes the place feel comprised of genuine people.
Moreover, you can make hundreds of anonymous posts on your own, but if no one reacts (and considers the thing/idea/joke uninteresting), they will still remain the only replies in your precious shilling threads.