Its because the scores haven't been affected therefore the commands can't tell if they have zero in the objective. you have to manual set the score to zero first
I have had this happen when I have both Blindness and Night vision on at one time.
...maybe the potion is giving you both effects?
I don't know if this helps but here is the crash report... If Notch or Jeb, or someone whp can help see's this
Crash report:
crash-2013-09-13_08.29.54-server
Yeah but do you know if there's any way to get my world back?
I just edited it and added screenshots. In the screenshots I am using the command that is failing to work. as you can see from the sidebar my score is one, however it doesn't give me the effect.