Sometimes my username appears twice after upgrading Ubuntu. There are a number of weird things that can happen, and I believe that they are usually related to this bug. Basically, one notification icon goes bad, and it shows the graphic of another icon. It’s very irregular, but luckily it is an easy fix.
The current workaround is refreshing the panel, which can be done with the following command:
pid=`ps -C gnome-panel -o pid=`
Thanks to Kees Van Mill for this workaround!