Swinging

Does anyone have a dog that gets real weird if you try to get on a swing? Can you swing with your dog in proximity?

So Vegas, my sweet, sweet Vegas who is usually so even keel, has never been one to get completely agitated at me unless it's out of excitement to do something or for something, but wow. Swinging brings out a Vegas I've never met anywhere else. Even if I ask her to sit and stay - or just stay - away from the swings, I am completely unable to swing with Vegas present. It's hard to describe her response. She pushes into me, blocks me, jumps incessantly at me, and even acts as if she would possibly use her mouth on my arm to pull me away. It's unreal. Someday I'll figure out how to get video of her reaction. In the meantime, I'm curious 1) What is the cause? and 2) Does anyone else's dog react this way about something? If so, what is that something that sets them off?