phpBB allows people to bump their topic or message, if there is no later post after a bump interval (set at 10 days by default).

However, if a given post was bumped once, it's no longer possible to bump it again after another bump interval has elapsed.

That behavior is perhaps intended. But the same user can flood with newer messages without that limitation anyways, and thus several consecutives messages from the same author can appear and fill the page.