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
Related issues
is duplicated by
Comments

As far as I know, you can't set your Spawnpoint into a solid block. When you try to respawn, the Bed looks for a space to spawn you on. When a spot is blocked, it's looking for other positions to spawn you. When all possible areas are blocked, your spawnpoint will be no longer set at the Bed.
Transparent Blocks e.g. Grass or Ladders can't block spawnpoints.