Blood River Outskirts: Poison Supplies quest bug

In the quest in Blood River Outskirts to poison the supplies at the elf camp, you have the option of talking to talking to Alberic first. I did this, and he offered me two options: a) Poison the supplies at the Vigilante camp or b) refuse to poison either camp.

I first selected option (a), and then I changed my mind. I inquired again about the poisoning, and on the second inquiry, he allowed me to choose again, and this time I refused to poison either. However, my quest tasks did not update accordingly, and I'm now left with a quest to poison the Vigilante camp that will not clear.