Trapdoors open/close when a block near them is updated

When you update a block next to a trap door it opens or closes it.

What I expected to happen was...:
I was expecting nothing to happen

What actually happened was...:
The trapdoor closes/opens.

Steps to Reproduce:
1.place a block down
2.put a trap door on it and open it
3.update a block next to the trap door