Click on red rectangle. This will change the width of a child (from 0 to 150), but this doesn`t make the parent to change width (even if it has width: auto).
It'd be easier to look into this if the test case didn't involve jQuery.
if i use display: inline-block instead of float: left, it will work at expected.
Confirmed with Google Chrome 17.0.927.0 (Official Build 108385) canary Mac OS X WebKit 535.8 (@99053).
Test case appears to be down. Could you ensure it remains available, or alternatively upload a html file?
Testcase is up again.
Created attachment 121243 [details]