My Guess, and I've read plenty of these is that the power to this circuit / lights does not
originate at the switch. There is enough EMF field to build up in the LED to have a visual release as the power goes by,
beside the fact that the positive side of any diode is still sitting on the hot + wire - it gets excited and it releases.
Not to mention poor design of circuitry and minimal material to get products out to the street.
At night I have a kitchen sink light that has a slight glow and haven't even investigated my own theory!
There are ten different types of Diodes (if one cares to read up -
https://byjus.com/physics/diodes)
LED
noun
- a light-emitting diode (a semiconductor diode which glows when a voltage is applied).
"light sources can be fluorescent tubes, optical fibers, or LEDs"