coasting to a stop

Hey guys, I ride a 1987 Yamaha Radian YX600. I've ridden it about 2000 miles since buying it (it has 9000 total). A weird problem has popped up recently. When I coast to a stop w/ the clutch pulled and downshifting, the rpms will drop below the idle point. If i don't give it some gas, it'll go...