Internal links on multipage post not working

Our student newspaper wants to create multi-page stories, with buttons at the top to link from page to page. We have it almost working.

The story we’ve put up this way is at https://www.whetstone.wesley.edu/2014…-beginnings-3/ . The problem is on the 1st page of the story. The buttons on the 1st page work properly when the story is first loaded. Once you use a button to go to the 2nd, 3rd, or 4th page, then come back to the 1st page, the buttons on page 1 to pages 2-4 no longer work. The links are getting messed up. What should be a link to https://www.whetstone.wesley.edu/2014…h-beginnings-3/3/ , for instance, becomes https://www.whetstone.wesley.edu/2014…h-beginnings-3/1/3/, which does not exist. Pages 2-4 work properly.