/entitydata doesn't change the pose tag on armor stands until you relog

I tried using the /entitydata command to change an armor stand's pose tag.
After using the command, nothing changed.
Later I relogged and the armor stand had changed its pose.
I tried it again, and the same thing happened.

Here's the command I used: /entitydata @e[type=ArmorStand] {ShowArms:1,Pose:

{LeftArm:[180.0f,0.0f],RightArm:[270.0f,15.0f]}

}