(Yes, I know there’s a bug report in game aswell, it’s been posted there already).
The quest Amidst Death, Life in Eastern Plaguelands is bugged. It has three objectives, to plant seeds in three different ziggurats. Two of them works perfectly, but the third (western) gives an error message when using the quest item. There were also 6-7 human paladins with weird names stuck in the same spot in the western ziggurat, presumably bots stuck trying to use the quest item over and over, unable to complete its objective. There’s a post from May 25th on the US forums about this quest, so it’s probably been bugged since Cata pre patch launch.
As a completionist, it does disrupt my questing experience when you need to abandon quest stories and leave them unfinished.