Commandblocks do not consider /scoreboard as a command

This is the same as my old one, I wanted to select 14w21b, but now I can't so I dealt with it.

What is the bug that you are experiencing?
Technically this doesn't affect many players, but can seriously affect mapmakers/redstoners (such as myself). I am trying to constantly power a commandblock (with a comparator clock) with this command in it: /scoreboard players set @a[331,44,458,0,score_pigRiding=0,score_pigRiding_min=0] pigRiding 1. For some reason commandblocks don't see /scoreboard as a command.

Can you try to recreate it?
I've only experienced this bug less than a minute before I created this report. This can happen rarely, so I don't know what caused this.

How did you fix it?
For some reason it fixed itself after I changed @a to @p.

That's all, I'm gonna end this report out.
Thanks.