Factorio Forums

If the player has an item from the quickbar in his hand, whilst a script executes swap_stack, and the stacks involved are both the one the player has in their cursor and an empty LuaItemStack, it will fail and return false.

Expected: Swap happens the same as it would when there is an item in the latter stack.

Video: https://youtu.be/ZfArzuu6SgA

Thanks for the report however that's working as intended. You're swapping an empty stack with an empty stack which is a no-op.