If you summon a ArmorStand with a head rotation set like

, it will work fine. But if you want to edit it with /entitydata or /tp command, it won't work. It's not a visual glitch because I quit and log back to the world and nothing happend...

EDIT:

Commands:

/entitydata @e[type=ArmorStand,r=3] {Pose:{Head:[45f,0f,0f]}} [WORK FINE]

/tp @e[type=ArmorStand,r=3] ~ ~ ~ ~ 45