Given that political parties, large companies and lobby groups have been actively employing people for years to post comments/"discussion" topics/etc on news pages, just like game developers and such have been "seeding" their message boards and such, I'm not terribly surprised.
I mean, it may seem unobvious or counterintuitive that even the obvious trolls work - as in "I'm smart enough to see this is nonsense" - but in the end, that's what most marketing is based on. A commercial is nothing but an extremely-obviously-biased "user comment" about a product, after all.
It's fascinating to observe and to see how this sort of process works, of course, and it's a good thing that we can tryy to qualify and quantify it. It's also horribly dangerous, in my eyes: with the advent of the internet, people seem more free but are, in fact, exposed to less contrary opinions than before: everybody tends to gravitate to groups/sites/... which conform (mostly) to their ideas. Combined with the fact that even obvious extreme trolls have an actual effect, seems to indicate people are more and more being reaffirmed into preconceived notions and polarized more and more...Which is a bad thing.
You can already see this at work in some ways with specific population groups amongst the youth these days. Where the political center is can change by country, but everybody is more and more convinced that their positions are "normal" and "centrist with a slight lean" and any opposition is far more extreme than it actually is. I'm not sure what political public debate will look like 20 years from now, but newspaper article comments and twitter don't point in the right direction, and there's unfortunately no clear and easy way to change that, without either limiting freedoms or pushing an agenda.