Comparator & Commandblock Output Lock

What I expected to happen was...:
The Comparator should turn off after commandblock has been activated.

What actually happened was...:
Comparator stays on until command block is broken and command is re-entered

Steps to Reproduce:
1. Place a commandblock down and inside it type "/say hi"
2. Then place a Comparator on the right of it (anywhere) and place another commandblock infront of the Comparator
3. Power the first commandblock and try re-powering it to get the comparator to turn off