If you shift click an item from the crafting GUI into your inventory, it will count two crafts towards that scoreboard objective.
Linked issues
is duplicated by 5
MC-30590
scoreboard incorrectly updates stat.craftItem scores when shift-clicking to craft
Resolved
MC-31305
Scoreboard system is buggy - doubles points
Resolved
MC-31533
crafting score gets increased by 2 if you shift click out of the crafting table
Resolved
MC-38821
Scoreboard bug while using stat.craftItem
Resolved
MC-39125
Shiftclicking a crafting recipe gives you double the points on the scoreboard
Resolved
Confirmed for 1.7.4.