It's come to my attention that chinese products with black-white color coded line cords are regularly miswired with black-neutral, white-live. These will regularly be marked as CE - their sole safety qualification.
Anyone buying chinese hobby-type products with mains connection had best be advised to check them out, The fault may simply be the polarity of the 3-wire line cord.
In any event, this characteristic can result in unsafe 'off' single pole mains switch function, single-fault fuse location.
Even such items as DIY led cabinet lighting can show 'glow in the dark' behavior, unless corrected. This is 'tingle' current flowing in the 'off' state.
RL