Whenever I click the above button in a thread with multiple pages, and the destination post being on a different page, I get this:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator,
sdw2@pair.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Since there is no "new post" on that page in that thread, it doesn't know that to do.. hence the error.
Hope this diagnosis helps the reparations.