Verified answer

So to clarify, usually when the airbag is turned off the warning light on the dash will extinguish once your passenger fastens their seat belt. Recently, however, the light doesn't turn off when you have a passenger that's buckled up?

In that case, it's probably a switch in the buckle mechanism of the belt that's faulty. I'd definitely have it checked out (preferably by VW), since it could prevent the airbag from deploying if you're involved in a collision.