Comment 56 for bug 12040

Confirming on Ubuntu 9.10 on 3 different machines, using the Main Menu applet instead of the default custom Menu Bar.
My current work-around is to install xvkbd and add the following to Startup Applications:
sh -c "sleep 5 && xvkbd -text '\A\[F1]' && xvkbd -text '\e'"

This will load the menu with Alt+F1 and then press Escape to close it right away. The sleep is necessary because sometimes the menu isn't available early, and the value is a trial and error heuristic that varies between 2 and 5 seconds from machine to machine.
It's similar to the work-around posted by las, just using xvkbd instead of xte to send events.

The bug is annoying because "non-techy" users usually greatly prefer the single-icon Main Menu to the default bar... and often one of first things those people remark is how slow Ubuntu is after clicking on the menu for the first time.