post parent category isn't working properly

The Post category isn't working properly.  If you take a look at the following theme here

http://www.olliemccarthy.com/themes/gonzo/

Click on music
http://www.olliemccarthy.com/themes/gonzo/?cat=28

Then Click on Indie
http://www.olliemccarthy.com/themes/gonzo/?cat=72

Out of the box Brew doesn't work like this
