Translated title is overwritten by the default translation title when editing a document section

Follow this steps to reproduce:

• In monolingual mode, create a new wiki page and set its title and content.
• Enable multilingual mode, and add a new language to the list of supported languages, say "fr" (the list becomes "en,fr"). Leave the default language unchanged.
• Edit the previously created wiki page and create the FR translation. Set a different title and add some sections (headings) to the content.
• Switch back to monolingual mode, changing the default language to "fr". Update also the list of supported languages to "fr".
• View the created wiki page. You should see the FR version. Edit and save one of the sections (you don't have to make any changes).

As a result, the wiki page has the original title (for the default translation).

The problem can also be noticed if on a monolingual wiki you change the default language (from the Localization administration section) and then edit a section page that has translations by default, like Sandbox.WebHome. Each time you edit a section of such a page the title of the page is reset to the title of the default translation for that page (en). Of course, the translation needs to have a different title in order for you to notice the difference.