/spawnpoint command only lasts one death

[alice-mkh]

Reproduction:

1. Start SSP world with cheats on
2. Walk away some and use /spawnpoint.
3. /kill yourself, you respawn at the point set in step 2, as intended.
   v4. Walk away some and /kill again, and you return to the world spawn with a "Home bed missing or obstructed" message

SSP bug because this does not happen in vanilla (you and /kill as many times as you want and it will return you to the point you set with the command in step 2)
This breaks some adventure maps that set custom savepoints, etc.