Pagination using sort criteria produces inconsistent page results

Not sure why the db would be doing this, but here's what happens:
We have a profile listing of churches: http://www.ecww.org/civicrm/profile?force=1&gid=9&reset=1
If you sort by City ASC, you'll get 3 churches in Vancouver at the bottom of page 2, and one church in Vancouver at the top of page 3.
Paging between 2 and 3 produces a different set of Vancouver churches on each page refresh.

My fix is to explicitly sort on all additional columns in sequence after the primary sort column. I suppose there could be a performance hit if the primary column or subsequent columns are too homogeneous and there's lots of data. Maybe there's a better way to do it with a single row number column or an id instead.

Change to CRM_Utils_Sort

function orderBy( ) {
if ( ! CRM_Utils_Array::value( $this->_currentSortID, $this->_vars ) )

{ return ''; }

$orderBy = array();
$direction = ' asc';

if ( $this->_vars[$this->_currentSortID]['direction'] == self::ASCENDING ||
$this->_vars[$this->_currentSortID]['direction'] == self::DONTCARE )

{ $direction = ' asc'; }

else

{ $direction = ' desc'; }

//primary sort column
$this->vars[$this->_currentSortID]['name'] = str_replace( ' ', '', $this->_vars[$this->_currentSortID]['name'] );
$orderBy []= $this->_vars[$this->_currentSortID]['name'];

//secondary sort columns; required for consistent results
foreach($this->_vars as $id => $sorter) {
if ( $this->_currentSortID != $id )

{ $sorter['name'] = str_replace( ' ', '_', $sorter['name'] ); $orderBy []= $sorter['name']; }

}

return implode(', ',$orderBy) . $direction;
}