Currently, when you have a command block with: <need redstone> <repeat> and with with a command like this for example “/testfor @a[r=5]”, if you get the command to read true that you are within 5 blocks from it, while also turning off the command by breaking the redstone torch near it, the command block will be in a sort of locked state (You can see that it is outputting a true output when turned off if you have a comparator next to it pointing away, it will stay lit up). The only way to unlock the command block would be to update the state of the command block, giving redstone power back to the command block, or to build your machine in a different way to avoid this problem.