Player cannot respawn on half slabs

I set my spawn by sleeping, later, I decided to decorate, so I surrounded my beds with half slabs as I have done before.

I expected to:
Respawn safe and sound beside my bed as usual

This actually happened
I was chucked into the ocean I spawned in and told "Your home bed was missing or obstructed" *This is on a server for the record

Steps to Reproduce this bug
1. Set your spawn in a bed
2. Surround bed with half slabs
3. Kill your character
4. Your bed will be missing or obstructed
*You were able to respawn on half slabs Pre 1.8.2 I believe