Double clicking on a item doesn't auto-stack the items in creative mode, but it still works in survival mode.
Double Click: Pick Up All Doesn't Work
Double clicking items in inventory to gather them into a stack only works in survival and not creative.
Double clicking spawn eggs doesn't collect other spawn eggs in inventory
Trying to gather-up all blocks/items of same kind in creative's survival inventory does not work (using the new function in 1.5).
Double Clicking in Inventory doesn't work (13w19a)
Inventory item shortcuts not working in creative