IE 11: Image doesn't scale down correctly within flexbox

Question

I'm trying to use flexbox to place two images in a column. In this case, the width of the div container is smaller than the width of the image. In Chrome the image perfectly fits into the div container, but it doesn't in IE, and I don't know why.

div.outer {
  width: 400px;
  display: flex;
  flex-direction: column;
  justify-content: space-around;
}

div.inner {
  width: 100%;
  border: 1px solid red;
}

img {
  width: 100%;
  height: auto;
}

<div class="outer">
  <div class="inner">
    <img src="http://placehold.it/480x360">
  </div>

  <div class="inner">
    <img src="http://placehold.it/480x360">
  </div>
</div>

https://jsfiddle.net/Yifei/16cpckqk/

This is what I've got in IE 11:

Answer 1

IE11 seems to have some trouble with the initial value of the flex-shrink property. If you set it to zero (it is initially set to 1), it should work:

div.outer {
  width: 400px;
  display: flex;
  flex-direction: column;
  justify-content: space-around;
}
div.inner {
  flex-shrink: 0;
  width: 100%;
  border: 1px solid red;
}
img {
  width: 100%;
  height: auto;
}

<div class="outer">
  <div class="inner">
    <img src="http://placehold.it/480x360">
  </div>

  <div class="inner">
    <img src="http://placehold.it/480x360">
  </div>
</div>

Answer 2

The accepted solution destroyed my sticky footers in ie. So I solved this disturbing issue with the following non satisfying "only for ie JS"... . The px value instead the "height:auto" did the trick for me.

 if(fuBrowser =='ie'){
  var img = $("#teaser img");
    img.each(function() {
    $( this ).css({height: $( this ).height()});
    });
  }