Hi Martin,
OK, I see the problem. After you used execution.setActivity() or moveTo(), you should save the modifed execution into database.
Generately, please do these operations in a Command, then jBPM 4 will commit the transaction automaticly. Please refer this:
processEngine.execute(new Command() {
public Object execute(Environment env) {
// ...
execution.setActivity(activityImpl)
//...
}
});