Div inside another div incorrectly occupies the parent width of the div

Question

Div inside another div incorrectly occupies the parent width of the div

Here is your dumb HTML / CSS question for the day ....

I have a div that contains two other divs. The container is set to display: box / -webkit-box / etc for folding the contained divs horizontally. The first containing div is some fixed content, and the second contains a bunch of other small tile fragments.

Here's an example: http://jsfiddle.net/dex3703/T2EZy/3/

A crappy chart is also shown (note that the 1000px shown is just an example - there is no width in any of the div containers):

Cheesy diagram