> nafiy
The bubbleing must be caused by the fact that you sprayed too close and applied too much paint at a time. Maintain at least 20-30cm, or spray across the object very very quickly (one push across the object in just about 1 second) to avoid this problem.
Also, wait longer than 24 hours before polishing. I even wait for a week, until the solvent is completely dry. What happens is that when you sand, you reveal a fresh surface, which may not be rock-solid. Polishing is less effective on a soft surface, resulting in dull surface.