Item duplication on creative inventory

What i was intended to do is:
1. Playing some stuff with my inventory
2. Pick an item and then hold number '1'on the keyboard
3. i pick the item in the middle of the transfer from 2 inventory slot and nothing happened

What i get was:
1. Playing some stuff with my inventory
2. Pick a random item
3. move the item from one slot to the other instanly by holding "1" on the keyboard
4. press the left mouse with the item right after the item is in the slot that my cursor in, it didn't pick it up, but instead of picking it up, the item duplicates