Keyframe and parallax

Question

I use Keyframe when my page loading. You can see when you reload the page, the div with the background come up with a opacity effect.

I use a parallax effect (https://github.com/nk-o/jarallax) on this background image but I have a problem when my transition animation is done and when I start to scroll : I have a shift/movement on my background image between these actions.

Why ?

Here's my JS FIDDLE.

.image {
  height:200px;
  width:400px;
  background-image:url("http://hdwallpaperbackgrounds.net/wp-content/uploads/2016/07/background-pictures-2.jpg");
  margin:50px;
  position: relative;
  background-repeat: no-repeat;
  background-position: 50% 50%;
  background-size: cover;
}

@keyframes fadeInUpImage {
  0% {
   /* transform: translate3d(0, 50%, 0);*/
    opacity:0;
    transform: translateY(50%);
  }

  100% {
    opacity:1;
    transform: translateY(0px);
  }
}

.m-scene .scene_element {
  -webkit-animation-duration: 0.80s;
  animation-duration: 0.80s;
  -webkit-transition-timing-function: ease-in;
  transition-timing-function: ease-in;
  -webkit-animation-fill-mode: both;
  animation-fill-mode: both; }


.m-scene .scene_element--fadeinupimage {
  -webkit-animation-name: fadeInUpImage;
  animation-name: fadeInUpImage; }