Statistical trends are not comparable when design and delivery change. Not all instrument items are equally important, and often some of them do not even match the rating scale. For example, adults tend to rate lectures lower than they rate experimental training exercises. In addition, rating a presentation is a contaminated act. The emphasis is often on excitement.
People like to have fun in training courses.
Many resent it when the trainer asks them to work hard, even for compelling business reasons. What we need is a clear index of the usefulness of the session, not whether it made people smile. Surveys tend to focus on what is wrong. The change-back effect is most likely. The most dramatic effect of training is no effect.