When you place a door in a 1 block high space, the block above the door disappears

When you place a door in a 1 block high space, the block above the door disappears.

What I expected to happen was that when you try to place the door, you would be unable to.

What actually happened was, the door destroyed the block above it and did not drop the item of the block it destroyed.

Steps to Reproduce:
1. Make a 1x1 block hole in a vertical wall.
2. Place a door in that hole.