html - Absolutely positioned flex item is not removed from the normal flow in IE11

Question

We have two divs with content and a third div that is a background with absolute position.

Container is a flexbox.

All works fine in Chrome and Safari, but Firefox and IE11 factors in the absolute positioned div, and distributes space between divs like there are 3 divs in a row.

I've made jsfiddle example. Is there any way to fix this bug? https://jsfiddle.net/s18do03e/2/

div.container {
  display: flex;
  flex-direction: row;
  width: 100%;
  height: 300px;
  justify-content: space-between;
  width: 100%;
  outline: 1px solid;
}
div.c1 {
  background: #aaeecc;
  width: 100px;
  position: relative;
  z-index: 50;
  top: 20px;
  display: flex;
}
div.c2 {
  background: #cceeaa;
  width: 200px;
  position: relative;
  z-index: 50;
  top: 20px;
  display: flex;
}
div.bg {
  background: #ccc;
  width: 100%;
  height: 100%;
  z-index: 0;
  left: 0px;
  top: 0px;
  position: absolute;
  display: flex;
}

<div class="container">
  <div class="c1">Content 1</div>
  <div class="c2">Content 2</div>
  <div class="bg">Background</div>
</div>

Answer 1

UPDATE: This issue has been resolved in Firefox (as of v52, released March 2017). The problem still exists in IE11.

---

Like you wrote in the question:

Firefox calculates absolute positioned div, and distributes space between divs like there are 3 divs in a row.

Firefox is considering the third div (.bg), which is absolutely positioned, an in-flow flex item and factoring it into its space-between calculation. (IE11 does this, too; Chrome and Edge ignore it.)

Clearly, this is not in compliance with the current flexbox spec:

4.1. Absolutely-Positioned Flex Children

As it is out-of-flow, an absolutely-positioned child of a flex container does not participate in flex layout.

Here are some workarounds:

Why not move the absolutely positioned div between the other two?

Instead of this:

<div class="container">
    <div class="c1">Content 1</div>
    <div class="c2">Content 2</div>
    <div class="bg">Background</div>
</div>

Try this:

<div class="container">
    <div class="c1">Content 1</div>
    <div class="bg">Background</div>
    <div class="c2">Content 2</div>
</div>

div.container {
  display: flex;
  flex-direction: row;
  width: 100%;
  height: 300px;
  justify-content: space-between;
  width: 100%;
  outline: 1px solid;
}
div.c1 {
  background: #aaeecc;
  width: 100px;
  position: relative;
  z-index: 50;
  top: 20px;
  display: flex;
}
div.c2 {
  background: #cceeaa;
  width: 200px;
  position: relative;
  z-index: 50;
  top: 20px;
  display: flex;
}
div.bg {
  background: #ccc;
  width: 100%;
  height: 100%;
  z-index: 0;
  left: 0px;
  top: 0px;
  position: absolute;
  display: flex;
}

<div class="container">
  <div class="c1">Content 1</div>
  <div class="bg">Background</div>
  <div class="c2">Content 2</div>
</div>