Kodonur Crossroads Mission Question

I was attempting the Kodonur Crossroads mission and I noticed towards the end that there were no more Taskmasters....anywhere. If you look on the map there are 6 cells you must open, but only 5 taskmasters. I even went to guildwiki to check for answers there and much to my dismay, the map showed the location of 5 taskmasters and 6 cells.

So I continue to play the mission and the stupid centaur will not let me into the last part. He keeps babbling about how there are still prisoners and how we must release them, yet, only 5 keys. I ended up searching the entire area and managed to kill literally every enemy in the entire mission, and could not find the last taskmaster or a key to open the cell.

Surely I am missing something here, because I seriously doubt ANet could have made a mistake that big and obvious, and besides, other people have obviously beat it because they have progressed in the game. WTH am I missing? Is this a client side glitch? Am I missing something? Or am I just a complete idiot.

Ok, don't answer the last question.

i'm pretty sure the number of task masters match the number of cells as i completed that mission on my ele on Sunday, maybe you just forgot to pick up the key? (which was what happened to me so i had to go running around looking for it for awhile)

have you tried the mission again since?

Its quite possible that you defeated a Taskmaster, he dropped his key and you didn't notice it. This happened to me as well untill after some exploring I found a key just laying on the ground.

The task master whos talking at start can be killed, did you get him?

~Doom