The command block saves the signal

below is the screenshot{}

In order to reproduce the bug, you will need such things as:

1. Command block
2. Redstone comparator
3. Redstone block (or any other block that gives a signal)

Order of execution:

1. We put the command block in repeat mode and write any executed command (for example '/say ABC')
2. We place a comparator next to it as in the screenshot.
3. We put a block next to the redstone command block, after which the spam '[!] ABC' will begin.
4. Break the redstone block (spam stops).

As a result:

The comparator remains powered up, although the execution of the command is completed.

 

Also, after all the actions, you can copy the command block by pressing the combination MW + CTRL, then place it on, you may notice that the signal is saved.