Traditional lacquers use alcohol solvents which will not affect enamels. Tamiya acrylics use an alcohol solvent system, and are therefore attacked by the solvents in your lacquer. No, Tamiya acrylics are not lacquers—they polymerize (called curing). Lacquers don't polymerize, they just dry.
Not all modern lacquers use an alcohol solvent system, so some of them may not do this, while others will. Those lacquers that are not alcohol solvent systems will, however, attack enamel paints.
Tyamada's advice about building up light coats will help, but you must allow for complete drying before applying subsequent coats of the lacquer.