title separator shows up double… why?

I’m guess this has something to do with the theme, but I don’t know a whole lot about coding, so I don’t know how to fix it… On my band’s web site, https://www.techniciansband.com, when you click on one of the pages (photos or downloads), the right-angle brackets that normally separate a page title from the site title show up twice. However, the title code looks like this:
<?php wp_title(); ?>
When I add something in the parentheses, like this (for example):
<?php wp_title('|'); ?>
that will also show up duplicated. In that case, it would be “technicians | | photos”.
Why is it doing that? I’m using the DarkNight 2.0 theme, modified a bit to make it work better for the layout I wanted. I have the HeadSpace plug-in installed, but it is set to leave the separator at whatever the theme sets it at.