In my plugin I disallow items to be moved between blocks using hoppers under some circumstances. For this I use InventoryMoveItemEvent, and cancel it if it needs to be. However, when an item is moved from a Hopper to a Crafter in 1.21, and the event is cancelled, the item is still removed from the Hopper but doesn't arrive in the Crafter.

I tried using two versions of Spigot I built locally with BuildTools, which had the same behaviour. However, using the latest build of Paper 1.21 does not trigger this behaviour, leading me to believe that this is some Spigot issue. My code has worked for years on all blocks, and this only happens on Crafters.