Hey there, everyone!
I have come across a problem with this theme: http://cinnamon-spices.linuxmint.com/themes/view/33.
This may be a problem with many themes on Cinnamon. The Glass-Shell Cinnamon Theme isn't fully compatible with Cinnamon 1.4. With the introduction of the new Expo workspace switcher, a user cannot simply add and subtract workspaces from the presented at default. For those of you who have recognized this problem also, never fear! I have a solution!
First, move the two pictures "add-workspace.png" and "close-window.svg" to the unpacked theme location Glass-shell/cinnamon directory:
cp /usr/share/cinnamon/theme/add-workspace.png ~/.themes/Glass-shell/cinnamon/
cp /usr/share/cinnamon/theme/close-window.svg ~/.themes/Glass-shell/cinnamon/
Second, open up the CSS file "~/.themes/Glass-shell/cinnamon/cinnamon.css" and add the following code:
Finally, save the changes and restart Cinnamon. Congratulations! You can now successfully add and remove workspaces to your heart's content!
Take care, everyone!