It seems broken and not completable a large portion of the time. The counter just gets stuck and stops moving, this has happened to myself and many of the folks I PVP with. More times than not it seems to stop at around 23/40, but I have had it go as high as 37/40 before it stops counting kills.
It would probably also help to have official word on what counts as a kill towards that quest. I have seen many hypothesis on the matter, from killing blows, doing the most damage, to doing any damage solo, but KB's if you are grouped. But I both have and have not gotten credit towards the quest in all those situations, so it must be bugged.
Please fix this, as it is one of the 4 quests that reward a Gladiator Rucksack, which we are after at least once a day... and many times, the only quest the board offers no matter how many times you decline and try again to get a different one.