The bug:
Pick block puts block you're "pick blocking" over to inventory. Occasional duplicates when grabbing from crafting menu.
What I expected:
Pick block or add new item (when selecting from crafting menu) over the item selected in hot bar.
What happened:
Occasional duplicate items or moves item being selected over into inventory.
To recreate:
Pick block (or select an item from the crafting menu) and add it to the hot bar OVER another item.