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.