rewrite_css creates error in http://www.androidacademy.com

[GoogleCodeExporter]

What steps will reproduce the problem?

1 In one tab, open up http://www.androidacademy.com
2.In another tab, open up 
http://www.androidacademy.com?ModPagespeedFilters=rewrite_css
3.Flip back and forth between the tabs; notice the visual difference in 2nd row 
icon background

What is the expected output? What do you see instead?

Expected: light gray background on second row of icons
Instead:     white background

What version of the product are you using (please check X-Mod-Pagespeed
header)?

0.9.11.5-293 

Please provide any additional information below, especially a URL or an
HTML file that exhibits the problem.

This problem is also repro'd on http://test.androidacademy.com/ but that site 
may need to become password protected soon.

Original issue reported on code.google.com by jmara...@google.com on 11 Dec 2010 at 12:26