Double shift clicking feature still in game

The double shift clicking feature was added in one of 1.5 snapshots but them removed.
I found that the feature is still in game.

To reproduce:
1.Create a clock with a command block.
2.Set the command block to give 64 items(example stone) picture 2
3.Open a chest
4.Put your cursor on the slot indicated by picture 3
5.Star double shift clicking very fast on the item, eventually you will get the effect and all items in your inventory will be put in the chest instantly
*The command block clock it's so you are always getting the item in stacks.

It's difficult to explained, if necessary I will do a video.