Comands Cannot target more than 1 scoreboard tag

if you put in a command block "/testfor @e[tag=1,tag=2]"
the last tag will overwrite all other tags.

What I expected to happen was...:
testing for BOTH tags

What actually happened was...:
the last tag overwrites all others

Steps to Reproduce:
1. summon 2 entities
2. Give them both a tag of "2" but only give one if them a tag of "1"
3. run the command "/testfor @e[tag=1,tag=2]" It will find both entities instead of only the entity with the tag "1" and "2".