dread: I've had a few 22 pocket rockets that have gone full auto on me from time to time. Once I got over the initial shock they were a lot of fun to play with and sometimes I could even trip them over into selective fire.
Most of the firms that make those pocket rockets, including Beretta, always seem to prefer the use of standard velocity ammunition for every day use and carry, apparently fearing the high speed stuff to be too hot for continued or daily use. Similar in thought to the S&W Model 19 when it first came out - shoot 38s in it all day and carry/shoot the 357s only when you have to. Problem with the pocket rockets though is that they don't always work that way.
I finally found out that the problem waas not the piece, in either instance, it was the ammo. The standard velocity stuff did not always lock the hammer back, be it an internal or external hammer, and the hammer would follow through with the slide and you would get full auto. When I went to the use of plain jane round nose solid high speeds (Rem Golden Boolets), the problems stopped in each instance. How so ever, if the one you had was badly abused it may have broken or been worked on. Sorry to hear that you had one that went bad. Mine are a ball to plink with and are very reliable. It gets dropped into my pocket on numerous occassions. Mikey.