Commands Work Then Don't Work

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I think there's something wrong with my Minecraft. I'm using commands in command blocks and I type my command in it works I copy the command, break the block put a put in the same command and I get an error and sometimes it even says unknown command. I'm in vanilla 1.8.4. Is there anything I can do?
/testfor @e[name=Skeletor] {Equipment:[{},{},{},{},{id:minecraft:golden_helmet}]}
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Why are some of my command blocks not working?
You may find that the commands you are trying to have the command block execute are not working. This may be due to the certain limitations the block has on what commands it can run successfully. Command Blocks will execute commands with an OP level 2 permissions.Can command blocks be broken?
The interesting thing about command blocks is that they cannot be destroyed by fire, and they have the same blast resistance as bedrock. They also cannot be broken in either survival or creator mode unless the host or operator grants permission.How to Use Console Commands in Don't Starve Together - How to Use Console in DST - Console Commands
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