Windows Vista 32 bit, Java Version 1.7.0_25-b16
When using Ctrl + Q on stacks in the survival inventory screen the blocks/items reappear in the inventory after closing the inventory and opening another inventory while still remaining dropped on the ground able to be picked up.
What I expected to happen was...:
The inventory stayed without the dropped stacks.
What actually happened was...:
The dropped stacks reappeared in the inventory while also being dropped on the ground
Steps to Reproduce:
1. In creative mode have some blocks/items in the survival inventory.
2. Use Ctrl + Q to drop some, then close your inventory.
3. Open another inventory (chest, furnace, beacon etc) without first reopening your inventory.
4. Observe the dropped items reappear in your inventory.
5. Close the inventory and walk over the dropped items to pick them up again so as to end up with 2 sets.
This worked with all the inventories I could think of, including hopper carts and shift-right clicking a tamed horse, except for villagers.
With villagers a dropped stack will "phantom duplicate" as subsequently picking up the dropped stack will cause it to go into the next free inventory slot while the original one appears empty until right-clicked (if it is/was a placeable block/item) or a non-player inventory is opened. If the player inventory is opened after closing the villager inventory and picking up the dropped stack the original slot will be properly emptied.
Similar effects can be had with just pressing Q, with some variation for different stack sizes.