LED's glow with power off. If the lights are on a two way switching circuit the live TPS cable may be run beside the feed cable for the lights. Induction can occur causing the LED's to glow or flash. This is more likely with low power lights such as stair or hall lights. This can be cured by installing a capacitor or relay
Premature Failure. A single failure is probably a faulty fitting, but if there is a series of failures it could be caused by residual power in the circuit. Even if the lights do not glow the power can severely shorten the life of the LED. Residual current can come from dimmers, sensors or by induction from a live wire.
LED flashes and dies during installation. The LED has been connected to a live driver.