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.
IceriIR
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.