Thumbnails missing after 3.1.2 upgrade

Everytime I update WP it breaks something in the Theme code. The actual image files are where they are pointed to, but I think the Lightbox gets broken. I have tried to reinstall Lightbox via FTP or auto install and WP 3.1.2 does not see it or cannot install it.

As my theme has a parent and child theme, the theme is not touched during update to WP. I would like to know the changes being made on each update of WP before I update it to know if it will break things or not.

Any ideas where I can find the change logs to maybe find out where to look for this bug?

Thanks,