After upgrading to 12.04 Gnome Classic amd64,every time I log on a new additional blank panel appears on the top and bottom panels - which I delete every time. In addition, the default panel applets are duplicated in the original panels.
Also the panels in the second screen are empty (in addition to the wallpaper being hidden).
As suggested by fossfreedomm I created a new user and the same behavior occurred.
I increased the height of the panels (24>36) and the added panels did not change.
If I don't remove the added panels and log off/on I get still another - they accumulate.
If I switch user instead of logoff/logon, the add'l panel do not appear.