On my Linux (Fedora 11, java-1.6.0-openjdk-184.108.40.206-27) category combobox is broken - it's very narrow and category names are not visible - see attachment (luckily it's possible to select it). It seems to work fine on Windows.
Broken category combobox sample
Thanks for reporting this! Anybody else having similar problems. Maybe also on other Linux distributions?
Same problem on Ubuntu 9.04