For some reason, "/gamerule commandblockoutput false" doesn't work.

Okay, here's the deal. I'm trying to make a single player map called "The Epic Tale of Epicness", and I keep doing the "/gamerule commandblockoutput false" command, it says "Gamerule has been changed" but it hasn't, I've done it in chat, and a command block itself. It still says "[@] blah blah blah the command executed good :)", and it's getting really annoying. I even did the alternative, "/gamerule sendcommandfeedback false", and it still didn't work. If I can, how do I fix it?