Q: I have used some contact cement to glue veneers, finished them, and several days later I had some bubbles where the adhesive had let go.

A: Did you know that contact cement is dissolved by the aromatic solvents in stain and lacquer? 

I suspect that this is what caused the problem. You will have to look for a different finishing system, perhaps water-based, or evaporate the solvents before they can break down the adhesive.