(Pages 5.5.2) Table of contents leaves first column blank when it gets too long

Hi everybody! I am experiencing a problem with my table of contents in a 2-column document. It displays fine at first:

But when I add enough content to start filling the right-hand column, it moves *all* the content into the right-hand column, like so:

I've looked in the inspector, but I can't find a setting that will correct this. Can anybody help me understand what I'm doing wrong?