Radius = 0 doesn't work

When i try to execute an Armor Stand [r=0] it doesn't gives me any message or output, it just happens nothing, only with [r=1] it is possible to track an Armor Stand, but sometimes i need [r=0] :/

Steps to Reproduce:
1. Summon ASor place AS
2. stay on the same block as the AS
3. /execute @e[type=ArmorStand,r=0] ~~~ [Command (e.g.: say hi)]