Are these bubbles hollow, ie, full of air, or are they solid lacquer all the way through? If the latter, it might be that your finger is getting in the stream of spray coming from the tip of the can, causing spatter. I finish with aerosol spray cans. When I first started I had a similar problem. Watch your finger. Also, you'll get a smoother finish with lacquer if you'll run hot tap water in a glass or cup and set the can in this for 10 minutes or so before spraying. Note that I said tap water. No heating up of water and can on the stove top.
