It would seem whoever did re-route them likely knew they were above that ceiling of the no fly zone. I think that the general perception was that the AA being utilized by the separatists were the shoulder fired variety that only has a ceiling of around 15,000 feet(ish) and not much thought was being given to the potential of more advance systems being used since they had not been up to that point.
I think it would be interesting to know who gave MH17 the redirection too and I imagine that it will come out eventually, but I really think that it won’t mean a whole lot. I doubt we will find that the traffic control intentionally directed the plane into that zone with the intent of getting it shot down. More likely it was someone who didn’t think it would be a risk since the plane was at such a high altitude (which is clearly a mistake).
I read earlier that MH17’s flight plan was officially cleared by Malaysian Airlines in Kuala Lumpur.