When cooking a recipe that returns a bowl it flings it out into the world instead of putting it in the bowl slot. An example recipe is the Pasta with Meatballs recipe.

This is an intended mechanic.

When an ingredient leaves behind a container, it is flung precisely towards the opposite side of the spoon, and can be captured by a Hopper or a Basket. You can use a Hopper to re-insert the bowl at the side, to auto-serve if you prefer.

If I made them be funneled into the bowl slot, it could end up clogging it, as well as being unable to handle two ingredients with different containers (for example, a recipe using both bottle and bowl ingredients). The container flinging lets the user choose what they want to do with such items.