[1.9] Spawnpoint y levels not respected in some cases

Partner Rank: 3
Verification Builds: New beta 1.9
Summary: If the play sets their spawnpoint when standing in a corner with a roof over their head, they will respawn on top of the roof instead of where they set their spawnpoint.
Repro Steps:
1. Create a new superflat world
2. Build a 3 block tall wall that turns a corner.
3. Place a flat roof at the top of the wall overtop of the inside of the corner.
4. Walk into the corner and run the command /spawnpoint
5. Walk away from the corner and run the command /kill
Observed Results: The player spawns on top of the roof above the corner
Expected Results: The player spawns where they ran the spawnpoint command, in the corner.
Screenshots/Videos attached: No.