That's weird. Like, kidinspace said, some LEDs stay on when the switch is set to off because they require so little current to power them and some current must still flow when the switch if set to off.
But what you're talking about sounds like the something has changed. Maybe the switch is faulty?
Something weird happened to me last night. I've got a LED festoon in my
Ibiza and when driving in the dark last night it would flicker on for a millisecond and immediately go off. This happened maybe 8 or 9 times in a 50 minute journey.