No credit for hard mode A Time for Heroes

So I tried searching for something on this topic, and nothing turned up, so if I just missed something, I apologize. I've killed the Destroyer twice on hard mode now, and neither time did I get credit in my book for finishing the quest.

Is this related to the fact that I haven't finished all the other missions on hard mode, or am I just missing something?

do you have another hard mode book on you when you are doing it? --if you do it will only update the first book. Do you have a HARD MODE book? or just the reg hero's handbook? (they are different)? You will NOT get points in a nm book for doing a hm quest/mission. (and vise versa)

I have the gold covered hero's handbook. The only other two books I have in my inventory are a normal mode Nightfall and a normal mode Flameseeker Prophecies. I know for a fact that the Hero's Handbook is updating because I finished two other hard mode quests, and they both updated.

have you tried talking to one of the guys you turn it in to? (if you dont have the book on you, you can pay 100g to get the pages filled in that you have done in the last 30 days).

None of the reputation characters offer the option (I've done it before, so I'm familiar with the process). The game appears to not be counting my hard mode kills all together. I'll try again and see if it registers. Pain Inverter makes it a fairly quick process, anyway.

I recommend do two tests.
1: like you said try again, make sure that the book is in the first slot of your inventory. if that doesn't work try:
2: storing this handbook in the xunlai chest, get another one and redo the mission.

If in 1 it doesn't get filled and in 2 it does then the handbook is bugged. If in both situations the book doesn't get filled then your hm questline is bugged. In both cases I suggest writing a support ticket to Arenanet.