Command blocks use to activate observer blocks but they no longer give them power.
Comments 5
Could not confirm for 1.2.13.54 on Windows 10. I used a non-repeating, unconditional impulse command block activated by a button. An observer detected the block update whenever a setting was changed, including whenever the command block changed its "Previous Output" field.
According to the wiki, an observer should detect only updates to the block or blockstate, not when it executes a command. This hasn't changed as far as I know. If you're certain the behavior has changed, please describe the following:
How your command block and observer are arranged, including which direction each is facing (a screenshot that shows this would be fine).
The settings of the command block, including its complete command.
How the command block is being activated.
https://i.imgur.com/32NRWFR.mp4
That use to power the observer block which would then power the redstone lamp but it not longer powers it.
Cleaning up old tickets: This ticket has not been updated recently (~1 year+) so is being closed as Cannot Reproduce. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines.
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Using a Comparator, or '/setblock' (etc.), is the best way it seems right now to obtain the status, yet you might need to force a delay in your circuit for it to give the expected result.