Reduced stacks of custom items delete excess

How to reproduce:

1. Create a custom item, with a custom "maximum stack limit" (ex: 16)
2. Place multiple stacks of items in a chest
3. Shift click, or shift craft multiple stacks of items, such that the new amount is greater than that of a stack

Observed results: The excess is deleted

Expected results: The excess items are split into a new stack, leaving the previous stack at its maximum value