I dont think this issue is an intended feature, when i turn on a copper bulb, save and quit and reopen the world, the bulb turns off. I have just tested this and it does the reverse as well, so it basically reverses the data of the bulb when leaving and reopening the world
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Here's a video of this bug on pocket edition 1.21.51
https://youtu.be/56aTU99DEFU?si=qIc625PQKProZamc
From what I've tested, this bug occurs when the copper bulb was initially powered by an observer and is lit. And when you save and quit and then reopen the world the copper bulb does, sometimes, turn off.
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We're tracking this issue in MCPE-29548, so this ticket is being resolved and linked as a duplicate.
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I'm unable to reproduce this bug. Are you using any add-ons in the affected world? Does removing them fix the issue? If not, then please attach the affected (zipped) world file. If the file size is too large, please upload it somewhere else and then link to it here.
On Windows you can use the Export world feature.
This issue is being temporarily resolved as Awaiting Response. Once the requested information has been delivered, the report will be reopened automatically.
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