Clay is not used if stack is moved out of a slot by stacking with another partial stack of clay.

Reproduction:

1. Have two stacks of clay, such as both add to less than 64/full stack.
2. Enter knapping screen using one stack of clay.
3. Double click second stack to combine stacks.
4. Any valid clay recipe does not consume any resources, the inventory slot that original clay was in is locked during crafting.