more than 1 tag in the selector with commands doesn't work

When I am searching for an entity for example with /testfor and in the Selector I write more than one tag, then there will be selected wrong entities.
For example /testfor @e[type=armor_stand,tag=1,tag=2]

There should only be displayed Armorstands who have the tag 1 and 2.

But it also lists Armorstands that have the tag 2 but not the tag 1.

Steps to Reproduce:
1. Summon two armor_stand
/summon armor_stand ~ ~ ~

{CustomName:"A",CustomNameVisible:1b}

/summon armor_stand ~ ~ ~

{CustomName:"B",CustomNameVisible:1b}

/summon armor_stand ~ ~ ~

{CustomName:"C",CustomNameVisible:1b}

2. Give them tags
/scoreboard players tag @e[name=A] add 1
/scoreboard players tag @e[name=A] add 2

/scoreboard players tag @e[name=B] add 2

/scoreboard players tag @e[name=C] add 1

3. Test them
/testfor @e[tag=1,tag=2]
Normally it should list only armor_stand A in the chat, because he has both tags. But it lists armor_stand A and B.

If you switch the two tags in the command
/testfor @e[tag=2,tag=1]
Here it should only find armor_stand A, but it lists armor_stand A and C.

Sorry for my bad English.