When a crafter is outputting into a full inventory, it places the result in the world as an item entity.

This is different to how droppers operate, where a full inventory prevents the dropper from moving items into the container, and no action occurs.

This is unintuitive to players, and while it could be worked around with additional Redstone to monitor the output container, would make the crafter more difficult to work with for non-technical players.

Steps to reproduce:

1. Place a barrel infront of a crafter.
2. Fill the barrel.
3. Set the crafter up to craft anything, and give it a redstone pulse.

Admittedly, there may be some complication fixing this since recipes can output a unknown number of items as well as additional items (such as buckets from a cake recipe etc) making a "check before craft" more difficult or performance intensive to do.