Golden Rule #1: Every unique URL should have a unique page Title
Supporting Rule #1: Posts or Articles that are paginated (for whatever reason) are unique pages in their own right, in that the content that appears when accessing that URL is different from the other pages.
Hypothesis: Having different paginated pages of an article/page with a shared title means you are giving search engines fuzzy signals as to what content is on what page.
Theory: If you confuse the search engines, you are likely to confuse your users. If it helps a user to view the title of a URL and have it indicate that it's page x of y, then that helps, correct?
So if for no other reason to provide additional help/clarification for your users you should consider adding the page number (or 'page #' etc) to the title. If this helps you in the search engines as well, then bonus.