Bug is related to MDL-18841 and MDL-17358.
Specifically see Tim's comment here http://tracker.moodle.org/browse/MDL-17358?focusedCommentId=68384&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_68384

This string (and probably others) in si_utf8/moodle.php:$string['pictureof'] = '$a?? ????????';

Creates the following PHP output:
[error] [client X.X.X.X] PHP Notice: Undefined variable: a\xe0\xb6\x9c\xe0\xb7\x9a in /lib/moodlelib.php(5433) : eval()'d code on line 1