When you type spawnpoint @p in a command block, and than activate it, it will show that spawnpoint was set, but when you die, you respawn in the world spawn.

What was supposed to happen:
Set player's spawn point to his actual position.

How to reproduce it:
Put the command block somewhere, set it's command to "spawnpoint @p" or "spawnpoint @a", than activate it using any redstone signal.