header.php doesn't work on localhost but does on live site

We have a memory leak in a production site that we are trying to locate within the very custom theme, and were using XDebug to track it down with NetBeans.

However, when loading the external site, there’s some sort of failure where it gets header. The PHP error is the so useful ‘syntax error unexpected end of file on line {last line of file} ‘ error in the theme’s header.php.

The odd thing is that the file looks perfectly fine, and works fine on the production server. It is precisely the same as the header.php on the live site, in fact *all* the files are the same except for WP-Config. We can get into the dashboard just fine on localhost because it doesn’t call header.php.

Any suggestions or ideas of what could make this different on localhost?