When you customize the post title, it's best to not select a field to set it. This function will set the title instead of using the settings.

Note: The fields you combine will not be automatically updated if your post field is changed from the WordPress posts page.

The built-in striphtml=1 parameter will remove all HTML from that value. But if there are specific tags you would like to leave, you'll need to specify exactly what to allow. Your shortcode for this example will look like [25 leave_html='em,i,b']. You can find more detail on using wp_kses in the codex.