Adding a User-agent to the database when saving a post

Hi,
I have a strange problem trying to add user agent to database, when posting. I just can’t simply do it, when I used the $wp_db or a casual mysql_query it simply adds a empty string to the new field in mysql.

I just can’t figure it out.. I even tried making a seprate php file, and the code works perfectly normal there.

Any ideas how to add this?
I wanted to have my browser/system displayed when displaying a post