Minecraft 1.8.2-pre6, Minecraft 1.8.7
When you use pick block with NBT (Ctrl + Mouse Wheel) on a command block with TrackOutput:1 and /gamerule sendCommandFeedback = false, and then place the command block it is some kind of bugged.
1. /gamerule sendCommandFeedback false
2. Place a command block and run a command which return any kind of feedback
3. Copy the command block with its NBT data
4. Place the command block
Now you cannot see any anything in the LastOutput line, but when you press the "X" you can see it.
I expected either that Minecraft ignores the gamerule when the command block has the tag TrackOutput:1 or that it sets it to 0 if the gamerule is false but also clears then the LastOutput