Certain block entities, when newly placed next to a power source, won't activate until they receive a block update.
Steps To Reproduce:
1. Place a command block to where it will be powered as soon as it is placed.
2. Type a command into the command block, e.g.: "say test".
> Notice the command block won't output "test" although it's powered.
3. Cause a block update next to the command block.
> Notice the command block now outputs "test".
This also occurs with dispensers, droppers, and note blocks.
See also:
MC-51340, it also happens if you got certain block entities with NBT data (e.g. a command block with an inserted command) and place that manually next to a power source, as well as
MC-31100 if you setblock certain block entities with NBT data where they would get powered, as well as
MC-80901 as falling block.
Code analysis by @unknown in this comment.
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duplicates 1
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Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Merging with MC-51340 as it's the same cause.
Please attach screenshots.