It's working for me on the following versions:
Ajax client:
Client Version: 6.0.8_GA_2661
Client Release: 20100820050930
Build Date: 20100820-0516
Zimbra Desktop:
Version: 2.0 (build 10514)
Granted, I'm a bit on the bleeding edge being inside the company but nothing should be significantly different between our 6.x versions to cause these issues. I have taken a few liberties within the zimlet code to automate some of its functionality, though. Perhaps those "hacks" are not behaving properly on your system.
Do you see any JavaScript errors in your browser? Also, any chance you can give me a test Zimbra account on your system? That should help me track this down and will be a lot easier than trying to install the exact version and trying to recreate it on my end. If this is possible, please send me email -- do NOT post to the forums.