Zero-count stack after copying Written Book from a stack

When I craft 2 or more copies of an original Written Book, then put them into the crafting grid while still stacked and make a second-generation copy, one of the first-generation copies becomes a stack of zero. Also, I end up with one fewer first-generation copies than I had before if the zero stack is indeed counted as zero (because when I start with 2 on the crafting grid, only 1 goes back into my inventory).