actually it often happens, whenever i wash my car at night and run it early morning, that abestos/brake shoes stick to rear brake drums, reason being rust, thin film of dust and the particles of brake shoes. get rear drums serviced.
btw, my car odo displays 23k n last time i got them serviced @6k. brakes are pretty okay but i'll get them serviced once a find some time in a week or so, hopefully.
edit: forgot to mention, brake pads soak water and in turn swell.