Yes this is the case in every event for the bonuts round. Why? because the bonut round is attached to a task. When you accomplish the task (by surpassing the quantity), the task is deleted and a new task is created with the same target (0/5400). This at least as far as I remember is how every event has worked in the past.
The reason the counter "doesn't" reset when accomplishing event goals but does "donut" goals is that exactly; the donut goals are just tasks, while the goals are cummulative quantities (ie, you get a reward after 10000, then 17000, then 19000). One of the replies above asks why not use the same mechanism-- the answer is because then EA would have to program the bonut rounds as goals starting from the last event goal. So if the last prize is at say 70000, then they'd have to add goals at 75400, 80800, and so on.. and possibly quite many given how many bonut rounds we all got this event. But then, they'd need even more hacks to hide those extra goals from the main event dialogs, etc, because they're bonus, etc.
Bottom line is-- it's not EA being greedy, mean, etc etc, it's just the way the bonut rounds are designed. They are single tasks. You complete one, a new one starts at 0.
My strategy is to leave plenty of pagans in my town and each time I approach the target, I stop trading fingers/books and start tapping the pagans. Least waste possible this way.