Comment 3 for bug 946867

I just found these packages of gnome-shell-extensions-common and gnome-shell-extensions-user-theme, version 3.2.3. They solve the issue; after restarting the shell one is able to change themes again. So I imagine it's more a matter of having the right version of these packages available for Precise somewhere rather than hoping to get a fix.

Sadly the upstream on extensions.gnome.org supplies only a version compatible with the soon-to-be-released gnome-shell version 3.4, which will not reach Precise in any way but through backports.