layout - Fill remaining vertical space with CSS using display:flex

Question

In a 3-row layout:

• the top row should be sized according to its contents
• the bottom row should have a fixed height in pixels
• the middle row should expand to fill the container

The problem is that as the main content expands, it squishes the header and footer rows:

HTML:

<section>
  <header>
    header: sized to content
    <br>(but is it really?)
  </header>
  <div>
    main content: fills remaining space<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    <!-- uncomment to see it break - ->
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    <!-- -->
  </div>
  <footer>
    footer: fixed height in px
  </footer>
</section>

CSS:

section {
  display: flex;
  flex-flow: column;
  align-items: stretch;
  height: 300px;
}
header {
  flex: 0 1 auto;
  background: tomato;
}
div {
  flex: 1 1 auto;
  background: gold;
  overflow: auto;
}
footer {
  flex: 0 1 60px;
  background: lightgreen;
  /* fixes the footer: min-height: 60px; */
}

Fiddle:

• http://jsfiddle.net/7yLFL/1/ (working, with small content)
• http://jsfiddle.net/7yLFL/ (broken, with larger content)

I'm in the lucky situation that I can use the latest and greatest in CSS, disregarding legacy browsers. I thought I could use the flex layout to finally get rid of the old table-based layouts. For some reason, it's not doing what I want...

For the record, there are many related questions on SO about "filling the remaining height", but nothing that solves the problem I'm having with flex. Refs:

• Make a div fill the height of the remaining screen space
• Fill remaining vertical space - only CSS
• Have a div to fill out the remaining height/width of a container when sharing it with another div?
• Make nested div stretch to 100% of remaining container div height
• How can I make my flexbox layout take 100% vertical space?
• etc