A couple of my WP installs were going haywire after the 3.5 update and I regretfully traced it to this plugin. Removed it and the problem vanished (just tried activating again to make sure). Specifically, while this plugin is active, I can't gracefully edit any page - it throws up this error when I hit the Update button:
"Warning: Cannot modify header information - headers already sent by (output started at /home/annebrnk/public_html/wp-content/plugins/duplicate-post/duplicate-post-common.php:112) in /home/annebrnk/public_html/wp-includes/pluggable.php on line 881"
It does actually save the page, and if you go back and reload then the changes will be there (same goes for duplicating). Since I'm not seeing any other reports of this then it might be a conflict with one of my other standard plugs:
Black Studio TinyMCE Widget
Email Address Encoder
Growmap Anti Spambot Plugin
Remove Double Space
WP Custom Titles