On JDS2, J2re1.4.2_10.

reproduce steps:
1. star mozilla
2. load the url:http://baseman.prc/jdk-applet-demo/1.4.2/demos/applets/GraphicsTest/example1.html
3. open the combo box by mouse
4. move the items by arrow keys
5. sometimes the mozilla crashes immediately with a log file
(the log file is in the attachment)