Comment 11 for bug 826089

I can confirm this is still an issue on Precise Alpha 1. The workaround is to first log into a GNOME Shell session, have 4 workspaces open in the workspace switcher, then log out and select Ubuntu 2D from the LightDM session menu. (Of course, if fewer workspaces are desired, you can also open fewer workspaces in GNOME Shell using this method. I don't know what would happen if 5 or more workspaces were opened since I didn't try that yet.)