Mysterious "Section 0" Editting

Conerning the edit buttons that appear to the right of each section
on a wiki page: My "first" section has two edit buttons. The left
edit button is for section 1, the right edit button is for section 0. I
immediately thought section 0 must be the first section, and
section 1 must be the second section. I didn't know why there were
two sections, so I clicked Edit for section 1, cut the contents, saved
it, clicked Edit for section 0, pasted the contents, and saved. When
I went back the page was just the same as before. When when I
went to edit section 0, it was empty, and section 1 was just the
way it was before. I added a section 2, and sections 1 and 2 work
fine.

The problem can be seen in action here:
http://cmugcs.sourceforge.net/wiki/index.php/Main_Page