Selecting a desktop will leave you with just the wallpaper showing and no way out other than to restart the window manager.
The fix for this is to install compizconfig-settings-manager:
sudo apt-get install compizconfig-settings-manager
We will use this to configure multiple workspaces instead of the obvious way, which is to right-click the workspace switcher applet on your desktop toolbar.
Important Note! If you have already configured multiple desktops in the obvious manner, make sure you undo that change and configure it back to a single workspace before we continue.
Now, to configure multi desktops open Compiz Settings Manager in Applications>System Tools>Preferences.
Next, navigate to General Options and open the Desktop Size tab.
Set up your workspaces how you want them there.
If you still have trouble, ensure that you configure the "obvious" place by selecting "Show only the current worskpace" and "1" for "Number of workspaces". In compiz-settings-manager "Horizontal virtual size" should be "4", the others "1".
Close the Compiz settings manager and your workspaces should behave properly again.