As of 1.12 Pre-Release 6, right-clicking an item stack into the creative mode item selector destroys one item each (MC-117858). This should be so in the "Destroy Item" too.
MC-118011
Right-clicking an item stack into the creative mode "Destroy Item" destroys the whole stack
Resolved
Duplicate
2
(Unassigned)
Confirmed
count, creative-inventory, item-stack, right-click
Minecraft 1.11.2, Minecraft 1.12 Pre-Release 6, Minecraft 1.12 Pre-Release 7
Retrieved
Isn't this a duplicate of MC-89217?