i would look in:

includes/languages/YOUR_TEMPLATE/english.php

and see if you have the code:

Code:
define('CHARSET', 'utf8');
the utf8 should be utf-8.

on v154, the charset is defined (for english) in:

includes/languages/english.php and has:

Code:
  define('CHARSET', 'utf-8');
but something is overriding it. and i'm guessing the template.

good luck.