[css-flexbox] flex-shrink being handled differently in different browsers

According to the editors draft of the flexbox spec
<http://dev.w3.org/csswg/css-flexbox/#flex-common>, the initial
`flex-shrink` value for flexbox items is 1 and the initial value for
`flex-basis` is `auto`.

I've linked to a jsbin where there is too much content to fit into a
containing box, and the way the shrinking is happening in Chrome/IE12 is
different from FF/Safari.

http://jsbin.com/xetinivozo/1

Since the initial `flex-shrink` value is 1, it seems perhaps Chrome and IE
are correct, but it's unclear how they've chosen the amount they're
shrinking.

Can anyone speak to which behavior is correct and why?