When cursed by Blindness you can't sprint

I had started making a game where you had to have blindness and night vision at the same time, while i had it on, i could not sprint, I do not know if it is a bug, or whether it is 'one thing' to blindness to maybe make it more realistic. The blindness and night vision came from command blocks that used the /effect command. I was using DTV97's handheld torch setup.