Trapdoors being used as a ladder replacement by one block

When I had a trapdoor in open position above a ladder, I was able to climb up the ladder and continue climbing on top of the trapdoor.

*What I expected to happen was to be stuck on the trapdoor *

What ended up happening was that I did not stop, but I continued to climb up the trapdoor

Steps to Reproduce:
1. Place any number of ladders in a straight line up
2. Place a trapdoor above the highest ladder
3. Place some more ladders above the trapdoor