Creative: Items dropped from hotbar slot 1 don't stack with slot 1

Items dropped from the hotbar while show survival inventory in creative mode, don't stack with the remaining items of slot 1, instead the next free slot is used.

Steps to reproduce:

• Creative Mode
• Open Inventory
• Place a stack of any item in slot 1
• While hovering over slot 1, press Q
• Close inventory
• Pick up the dropped items
  -> Voila, slot 2 is used