When having a plugin that cancels BlockPlaceEvent, if you place a bed on top of a crop in a dark room, it will be duped.
I suspect it is because the block placement updates the crop below and because it is in a dark room, it is dropped. However, the event is cancelled, so nothing really happens, but because the crop was already dropped, you can do it again and again resulting many crops being dropped.

It seems like this bug is from at least 1.17, as can be seen in this patch that was made for WorldGuard a while ago:
https://www.youtube.com/watch?v=OZ99W8jlnfY&t=3s

(You must do it in a dark room, otherwise it will not occur)