The $zero_space = "\xE2\x81\xA0"; (see below) seems to be creating ? utf characters in the two up diff view.
I'm seeing the same issue on secure.phabricator.com.
Adding a space before the unicode seems to fix it. $zero_space = " \xE2\x81\xA0";
Seen in Chrome v 33.0.1750.154 m on Windows.
Looks fine in Firefox 28