Using the 1-9 hotkeys to move an item to the 1-9 slots used to move the item there in any inventory (moving items that were already there to a different slot if needed), only not working if the player's inventory was full. However, as of the 15w44b snapshot, this no longer works; it will now only put the item in the slot if it is free.

Steps to reproduce:
1. Sort your inventory so you have any item in your first slot.
2. Enter an inventory, such as an Anvil, Crafting Table or Furnace.
3. Produce an item in their output slots (e.g. by crafting, smelting or combining).
4. Hover over the item and press the 1 key.

Video: https://imgur.com/GN2itSo

Expected Result:
The number 1 slot is replaced with the item from the inventory & the item originally in the 1 slot will enter the second slot.

Acquired Result:
The item stays in the inventory & the item currently in the first slot stays there.

Ways to Fix:
Revert to the behaviour of <1.8.8 & <15w44b, pretty sure Grum has been fixing a few bugs associated with hotkeys, stacking behaviour and inventories recently - so he must have made a change somewhere that produced this bug.

Other Steps to reproduce:

• Place valid recipe contents in crafting grid
• in 1.8.9
  • Pressing hotbarkey of slot with item same as crafted item will add the item to the hotbar
  • Pressing hotbarkey of slot with other item as crafted item will swap empty hotbar slot with occupied and place crafted item to the hotbar
  • Pressing hotbarkey of empty slot places item there
• in 1.9-pre4
  • Pressing hotbarkey of slot with item same as crafted item will add the item to the hotbar (No longer works)
  • Pressing hotbarkey of slot with other item as crafted item will swap empty hotbar slot with occupied and place crafted item to the hotbar (No longer works)
  • Pressing hotbarkey of empty slot places item there (Still working)