I had the same problem with one of my sites… looks like a bug.
It is a bug in the theme I used. Now I have to start all over again and find another theme.
No, it’s not a bug in WP, but there may be conflicts with some plug-ins or themes. This thread tells you how to start troubleshooting your site:
http://wordpress.org/support/topic/troubleshooting-wordpress-35-master-list?replies=4
@neilson64 – if you need help, please start your own thread.
thanks, I did that and I know it is the theme. 🙁
Yes, some themes may have problems with WP3.5 and if the theme developer has not fixed them, you may need to find another theme.