In creative mode, if you destroy a block that an item is attached to, the item will drop.

Steps to reproduce:  

1. (If you haven't already) Create a new world and set it on creative mode. 
2. Go into your creative mode world. 
3. Go into your creative inventory and get any item that can attach to a block, like a sapling or a torch.
4. Place the item down. 
5. Destroy the block underneath.
6. Instead of destroying the item like usual in creative mode, it drops, allowing you to pick it back up.

This also happens if you destroy a block that a torch is on the side of.