Java 1.8.0 Build 121 Win7 x64
When doLimitedCrafting is set to true it is possible to duplicate items in both the personal crafting and crafting table boxes.
This works with both stackable and non-stackable items.
To reproduce. set doLimitedCrafting to True. For non stackable items, 2 will work. For stackable items, fill all slots with the item.
Click and drag like you would be splitting a stack. upon dropping the item in its original slot. double click. That item is now duplicated.
Video Demonstration https://www.youtube.com/watch?v=8dAQJp--k6w