Steps to reproduce (You can swap the leaves, it'll work the same way):

1. Place Dark Oak Leaves on the ground
2. Remove it from the inventory
3. Pick Acacia Leaves and put it somewhere in your inventory (not in your hand)
4. Pickblock the previously placed block

What should happen:
The dark oak leaves are properly picked as any other block.

What atually happens:
The acacia leaves are put in your hand and the name "Dark Oak Leaves" is displayed above.