Seems to me that your collision polygons are messed up. They wiggle (animated) arround the origin.
Meaning, if you change to another animation it happens that the player is caught up in the solids. The platform does not know that on the moment you change animation. It finds out when you move, in your case, when you jump from idle. Now the platform should be stuck, but it has an automated 'push out of solids' mechanisme. And that is what you see happening. This mechanisme is essential. So ...
Be more carefull with the collision poligones, when working with animations.