The /Spawnpoint command does not set spawn

The /Spawnpoint command doesn't work, if it's triggered by a command block.

The command should set your spawn, but it didn't work. I am sure that this is annoying to map makers, as I was making a map myself when I got this bug.

When I killed myself, the chat box said, "Your home bed was missing or obstructed."

Steps to Reproduce:
1. Use a command block and have the command block say "Spawnpoint (x y z)"
2. Use redstone to power it