If it does this when the timer is off then it could be an issue where the timer is drawing enough power to run and that is just enough to dimly illuminate the LEDs. This is a common issue with wireless dimmers and LED lights that can also be caused by how the neutral wiring for that circuit is wired. If the light stays on, when the cord is physically unplugged, then it sounds like it has a capacitor in it that is very slowly discharging to the LEDs. If it doesn't discharge completely, within a minute or so, then I would contact them and get it replaced.