Crafting Issue

When using shift-click in the crafting bench, I had an issue where the left-over ingredients were not correct proportionally. I was trying to make two fishing rods so I took two planks and made 4 sticks and I got 6 string. When I shift-clicked the fishing rod, I only got 1 fishing rod and then instead of 3 sticks and 2 string I had 2 sticks and 4 string.