/spawnpoint bug?

Put the summary of the bug you're having here
When I set the respawn point on top of a pressure plate it just teleports me to the Main Spawn is this a bug? or just a feature?

What I expected to happen was...:
Respawn me on top of the pressure plate

What actually happened was...:
It re-spawns me to the main spawn-point instead of the spawnpoint I set.

Steps to Reproduce:
1.Stand on top of a pressure plate
2. ...type /spawnpoint
3. .../kill
4. you respawn on the world spawn.