After death (/kill) Command Blocks cannot be interacted with until closing and reopening the world, however they can still run their command. Also, placing a new one does not animate the hand nor play a sound, while breaking them plays a sound and animates the hand, but no to few particles appear.
Steps to reproduce:
1. Place a command block.
2. Use the command /kill.
3. Return to the command block.
4. Right-clicking performs no action until relogging.