The patch for MDL-15501 was erroneous.

You wrote (in blocklib.php, blocks_print_adminblock(), lines 952+)
+ $strblocks = '<div class="title"><h2>';
+ $strblocks .= get_string('blocks');
+ $strblocks .= '</h2>';

whereas it should be
+ $strblocks = '<div class="title"><h2>';
+ $strblocks .= get_string('blocks');
+ $strblocks .= '</h2></div>';