The bug
When a Crafter attempts to output multiple items at ones in a Composter, all the items are composted as a single one.

To reproduce:

1. Place a crafter facing downward directly above a composter
2. In the crafter, put a stack of cocoa in the top middle slot and two stacks of wheat in the two top corners (this will output eight cookies)
3. Place a button on the crafter
4. Press the button
5. Open your debug screen (F3)
6. Look at the "level" state of the composter
   See if the composter went up more than one level (normally 8 cookies would raise it a few levels)

What I expected to happen was...:
The composter increasing several levels at once

What actually happened was...:
The composter only increased one level or none at all, as if it were composting a single cookie