About c_freecrafting()

Please watch the video and pay attention to the amount of the boards.

I use c_freecrafting(). I have 10 boards and I make a chest. The boards become 7 and several seconds later the 3 boards are back.

But I cannot build the chest until the 3 boards are given back to my inventory.

Is that working as intended? Why the 3 boards must be used even if with c_freecrafting()?