Special:RenameUser has two final submit buttons on its form: one for "submit", and the other for "show block log for user".
However, FormSpecialPage doesn't allow this: it only lets us have one submit button at the end. Others have to be in the main form table structure, making porting RenameUser to FormSpecialPage difficult.
It should be possible to add multiple final submit buttons within the "usual channels" of getFormFields().
(That said, maybe the "show block log" button should actually be a hyperlink?)