From @SalixAlba:

1. Start editing a page with the wikitext editor, e.g., [[Example]]. The main heading at the top of the page will be "Editing Example".

2. Now switch to VisualEditor. The main heading will not be changed.

3. Make an edit and save. This does not change the main heading it is still "Editing Example", when it should be "Example".

Reloading the page sets the title back to normal. Note it also temporarily changes the <title>...</title> tag, of the page.