MC-14586You can pick up command blocks with any pickaxe
Edit by EvilSeph from Mojang:
This bug here is actually that an item is dropped when a pickaxe is used to hit a Command Block and has nothing to do with Silk Touch.
I was wondering if you could still pick up mushroom blocks with silk touch, and since it was my test world, I had a command block in my inventory, when it dawned on me. I placed the command block down, went into survival, and instead of the command block breaking and not dropping anything, a command block was dropped.
This can be dangerous, if there is a "rogue command block" amok on a server. If the server has currency, a player could sell this block to a person and get a huge load of cash, meanwhile the player can't do anything with it, for you need to be opped and in creative mode.
Hope this gets noticed! 
Created Issue:
You can pick up command blocks with silk touch...
I was wondering if you could still pick up mushroom blocks with silk touch, and since it was my test world, I had a command block in my inventory, when it dawned on me. I placed the command block down, went into survival, and instead of the command block breaking and not dropping anything, a command block was dropped.
This can be dangerous, if there is a "rogue command block" amok on a server. If the server has currency, a player could sell this block to a person and get a huge load of cash, meanwhile the player can't do anything with it, for you need to be opped and in creative mode.
Hope this gets noticed!
EvilSeph (Warren Loo)
You can pick up command blocks withsilk touch...You can pick up command blocks with any pickaxe
I was wondering if you could still pick up mushroom blocks with silk touch, and since it was my test world, I had a command block in my inventory, when it dawned on me. I placed the command block down, went into survival, and instead of the command block breaking and not dropping anything, a command block was dropped.
This can be dangerous, if there is a "rogue command block" amok on a server. If the server has currency, a player could sell this block to a person and get a huge load of cash, meanwhile the player can't do anything with it, for you need to be opped and in creative mode.
Edit by EvilSeph:
Hope this gets noticed!
I was wondering if you could still pick up mushroom blocks with silk touch, and since it was my test world, I had a command block in my inventory, when it dawned on me. I placed the command block down, went into survival, and instead of the command block breaking and not dropping anything, a command block was dropped.
This can be dangerous, if there is a "rogue command block" amok on a server. If the server has currency, a player could sell this block to a person and get a huge load of cash, meanwhile the player can't do anything with it, for you need to be opped and in creative mode.
Edit by EvilSeph:
Hope this gets noticed!
Edit by EvilSeph from Mojang:
This bug here is actually that an item is dropped when a pickaxe is used to hit a Command Block and has nothing to do with Silk Touch.I was wondering if you could still pick up mushroom blocks with silk touch, and since it was my test world, I had a command block in my inventory, when it dawned on me. I placed the command block down, went into survival, and instead of the command block breaking and not dropping anything, a command block was dropped.
This can be dangerous, if there is a "rogue command block" amok on a server. If the server has currency, a player could sell this block to a person and get a huge load of cash, meanwhile the player can't do anything with it, for you need to be opped and in creative mode.
Hope this gets noticed!
Silk touch works on command blocks --> Confirmed in 1.5.1
Confirmed in 13w16b.
Even though it says this problem is resolved in 13w17a, Xisuma proved that this has to be reopened, or Warren has to fix this in a "b" snapshot...
Reopened. But you don't need a silk touch pick. Normal pick will do the job just fine.
Oh, so I've been chasing the 'silk touch' angle and getting nowhere, when it is actually a pickaxe at all drops a Command Block item so obviously my fixes didn't work (I didn't test this one, it seemed so simple...). I've edited the ticket and will fix this bug.
Sometimes the problem is staring you right in the face, but you don't see it. xD