Why do I get issues with content appearing after migrating site from subfolder to the root?

If you set up your website in a subfolder, and decide to move WP to the root on a live server, ensure your next steps will be correct. If you do it incorrectly, you stand to lose all your widget settings, some file links and so on.
There are many paths stored away in the database, in various forms, and catching them all can be difficult. To avoid that serialization issue, you have to read the article When Your Domain Name or URLs Change