It's simply a gear meshing issue, (once the fix is done). All sleds with mechanical reverse have to mesh, and the way Yamaha does it, it's not always going to happen perfectly. Since there is not a spring loaded mechanism the gears have to mesh when you pull the handle, or push the button in the case of the Phazer, because a gear is a gear the teeth are not always perfectly aligned. The rocking simply moves the gear a touch and allows it to engage. I had a Polaris with the lever activated reverse that had a spring loaded mechanism, it sucked, and it ground the gears so much that they need to be replaced. It would pop out of reverse all the time. Bottom line is I prefer the Yamaha method as it may require a little hip movement here and there ar least it doesn't grind. Before someone says RER is perfect, it's not, I've seen RER sleds stall many times so the only sled that has a perfect reverse system is one that doesn't have reverse at all. The human lift and carry method.