If uploading the files doesn't work, try commenting out the line that displays the buttons, and see if it cleans up the garbage. It's in PersonalMessage.template.php -
// Send, Preview, spellcheck buttons.
echo '
<p><label for="outbox"><input type="checkbox" name="outbox" id="outbox" value="1" tabindex="', $context['tabindex']++, '"', $context['copy_to_outbox'] ? ' checked="checked"' : '', ' class="input_check" /> ', $txt['pm_save_outbox'], '</label></p>
<p id="shortcuts" class="smalltext">
', $context['browser']['is_firefox'] ? $txt['shortcuts_firefox'] : $txt['shortcuts'], '
</p>
<!--p id="post_confirm_strip" class="righttext">
', template_control_richedit_buttons($context['post_box_name']), '
</p-->
<input type="hidden" name="', $context['session_var'], '" value="', $context['session_id'], '" />