Sorry for the delay.... been working over the weekend...
Has the dog done a lot of retrievel work with the dummy? If it has, then it's a possibility that the dog has a very high reward reinforcement in this specific exercise. Constant retrieval is a self rewarding exercise that increases behaviours with every retrieve. The more you do, the greater the increase in behaviour. Eventually, just the sight of the dummy illicits a chemical response in the dogs brain and it becomes stimulated. The very first retreive will be like dropping a bomb of stimulants into the dogs brain and it literally cannot control itself.....
If the dog has learnt some level of control around a tennis ball, it simply places a lower value on the tennis ball, and isn't as stimulated in this exercise so it can control itself.
Without actually seeing your dog in person I'm using experience over observation here, but I'd recommend stopping all dummy work for the time being and taking your dog back to basics of control. Your dog needs to learn that it has to control itself in every situation. I'd recommend that it must never be allowed to jump up at anyone at any time. This also means you cannot encourage the dog up fir a cuddle! (A dog has four feet, and they should all be on the ground). Maybe your dog has figured out that certain exercises only happen in certain environments, requiring separate behaviours/rules in those environments (another guess). If this is the case, your dog is constantly trying to adjust its behaviour to fit any number of environments, so it's in a constant state of stress.
A dog should be under control at all times in any environment, and this is achieved by keeping the basics of control the same, all the time. I've always gone with the maxim of 'control from the kennel' meaning: my dog is expected to be under my control at all times. I do not take a dog to an obedience club to 'do obedience' nor do I take a working dog to the field to 'do retrieving/recall'. I do all these things everywhere, from the point of leaving the kennel to putting the dog back in the kennel.
Traditionally, some trainers do a lot of hunt work and little to no control work because they think too much control work diminishes a dogs 'drive' to hunt. Absolute tosh. A well bred, well selected dog has instinctive drive, there should be no need to have to 'build drive'.
If your lab is highly stimulated, then what you should do is strip it all right back and regain control. No need for dummy retrieves, sounds like your dog has enough 'drive' for that already!
As with all things dog, I say potato, you say...... and the only thing two dog trainers will agree on is the third one is wrong.....
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