Incorrect window closing

On Ubuntu Lucid, with AWN managing my open windows, I have a launcher for Chromium. With two instances open, I try to close one, and the wrong one closes. Steps to repeat:

1.) Create Chromium Web Browser Launcher
2.) Launch Chromium instance from AWN Launcher
3.) Navigate to engadget.com
4.) Launch 2nd Chromium instance from AWN Launcher
5.) Navigate to google.com
6.) From right click menu, minimize google.com instance.
7.) From right click, close google.com instance.

At this time, I've seen the engadget.com instance close consistently.

System Setup:
 - Chromium 6.0.472.62 (59676) Ubuntu 10.04
 - AWN 0.4.0
 - Chromium Launcher command: chromium-browser %U

Thanks,
kenny3794

Update: I was able to recreate with OpenOffice.org Calc running 2 generic spreadsheets.