I hate fake falls and screwy jumping responses and I've assiduously trained everyone I've ever worked with NOT to take baloney falls if a technique is no good. But every now and then something happens so easily and produces such a startling result that I know there's more to this stuff than you might really understand just by seeing it happen.
Taiji people dislike it too. And when startling results happen it can surprise the hell out of them. How to train to consistently reproduce the startling results takes taiji people far afield . . . even here to an aikido forum.
Unfortunately, one of the video links referenced in this thread from 2003 is no longer available, but the discussion is still interesting.
One post in particular from this thread is worth considering:
I think there are a couple of different scenarios regarding the hop. One, as Jerry suggests, is a voluntary hop that one does when one knows that an opponent or push hands partner has you at a disadvantage, and you're about to be launched. It's a way of maintaining your frame, and quickly re-establishing your equilibrium. The other scenario is an involuntary hop. This can happen once one has been "led into emptiness" by your partner, and there is a sensation of disorientation where you're not quite sure of your vertical orientation, and it literally feels as though one has fallen or stepped into a hole (which is another way of translating "luo kong"). In this case, even though both feet are on the ground, your legs involuntarily stretch out as you try to "find" the ground, as it were. If the opponent adds just a little lift to your frame at this moment, you'll propel yourself back in a hop, or series of hops.
Just as it can be a bad habit to hold your ground no matter what, I imagine the defensive hop can develop into an unconscious habit with negative consequences. The hop reminds me a little of what I learned in jujitsu years ago, called "sutemi." Beginners learn mat rolls, falls and solo flips, working up to airborn versions of the same. Later, you learn that the solo airborne flips you've been doing are basically your half of what happens when being thrown by a partner. In practice, partners often "help" each other by doing sutemi while being thrown. As a beginner, I don't think I was even aware of this phenomenon until the sensei once called me to the mat during a school demonstration to perform a throw on me I hadn't yet learned. I went up and grabbed his gi as normal, and he looked at me and said quietly, "Don't sutemi." My mind kind of went blank, and the next thing I knew, I had hit the mat faster and harder than I ever had before. With this little demo, he made it clear to me that he didn't need my help for his technique to work.
With respect to "hopping," I tend to think it follows more particular styles
of taiji than whether the taiji is "southern" or "northern" Chinese. Hopping happens in Beijing as well as Hong Kong or Shanghai:
In general, I've seen much more "hopping" in connection with Yang and Wu (Jianquan) lines of taijiquan than with Chen.