Put the summary of the bug you're having here

What I expected to happen was...:
That when I opened a trapdoor while standing where it would go, I would be able to walk through it.

What actually happened was...:
I got pushed down by the trapdoor into the blocks below it and couldn't get up unless I opened the trap door.

Steps to Reproduce:
1. Place a trapdoor at the height of 1 block (in the air) or below you with a block open below it.
2. Open the trapdoor while standing on it.
3. .Close the trapdoor. I had a canal below the trapdoor and almost drowned.