I’m seeing the same behavior since the update to 1.2.5 today. Tried deleting the title and replacing it, but any text in the title field is duplicated.
Not using an SEO plugin. On latest version of WP. My dev site, which is still on GP 1.2.4 does not have this issue. Just updated the dev from 1.2.4 to 1.2.5 and the duplicate title issue now happens.