I don't know if this will help any, but the version I have installed in Feisty that works properly is 0.98~svn20070409-0ubuntu1, and the other listed available version (which is also what I get with apt-cache show) is 0.6.3~svn20070207-0ubuntu3, so it is a third party package of the new gnome-main-menu and not the old one in the repos. I don't remember where I got it though, and can't figure out how to find that out if it's possible, but I believe it came from the Tips & Tricks section of the Ubuntu forums. I'm sure it's too late to get whatever fix it is from that package, but maybe it'll be useful for a fix for an update after release, if found?
I don't know if this will help any, but the version I have installed in Feisty that works properly is 0.98~svn2007040 9-0ubuntu1, and the other listed available version (which is also what I get with apt-cache show) is 0.6.3~svn200702 07-0ubuntu3, so it is a third party package of the new gnome-main-menu and not the old one in the repos. I don't remember where I got it though, and can't figure out how to find that out if it's possible, but I believe it came from the Tips & Tricks section of the Ubuntu forums. I'm sure it's too late to get whatever fix it is from that package, but maybe it'll be useful for a fix for an update after release, if found?