I personally can't explain the bounce back, but if I had to try to explain the rest: due to the hydrogen bonding (intermolecular force between water molecules), water has fairly high surface tension. When a water droplet is dropped into the water, it has enough kinetic energy to overcome the surface tension, and breaks through. When the smaller droplets bounce back, you'll notice they sort of bounce off and then "sit" on the surface for an instant before being absorbed into the rest of the water. I believe what's happening here is that the "bouncing" droplets have too much kinetic energy for its water molecules to form stable hydrogen bonds with the water molecules of the larger body of water, but not enough to break the surface tension of the water. When it slows down/stops sufficiently, the hydrogen bonds can be formed between the molecules in the droplet and the molecules in the rest of the water, at which point it is subsequently absorbed.