/execute Command Bug with /tp

When I run the command "/execute @a ~ ~ ~ /tp @e[type=Chicken] ~ ~ ~-10"
The chicken I spawned in with a spawn egg moves 10 blocks from it's current position, not 10 blocks from the player.
I hope to see this fixed as it is required for the mini game I am creating.
Thanks - Bom
(If I have written this command wrong and this isn't a bug, please let me know the correct way of putting it)