I just discovered that WP 3.5 no longer adds the "title" attribute to images when they are inserted. Instead it adds the "alt" attribute which is probably preferred for SEO purposes but doing so unfortunately breaks this plugin's ability to add titles to enlarged shadowbox images.
If there's an easy fix, please let me know. I'm sure the plugin files could easily be modified to accommodate this change but I'd prefer not to do this since it will need to be redone with every plugin update.
sivel (plugin author) - If you're not already doing so, I propose that the Shadowbox Title plugin be modified to push the image "alt" attribute to the anchor tag "title" attribute if the image's "title" attribute does not exist.