Compass Not Pointing to Actual Spawn Point

After creating a new survival world in 1.7.2, I had just build my house, acquired a bed, and laid down to reset my spawn point to my house. Now, I do use SSP commands, so after I did this, I gave myself 1 compass to take with me while I went mining.The compass doesn't point towards my house, it points a little bit diagonally away from it, but if I'm right, shouldn't it be pointing towards where I slept?