That is correct. Do you have multiple languages on your forum?
You can force the , by editing this file adminsourcesclassesclass_localization.php using ftp or file manager.
find
public function formatNumber( $number, $places=0 )
{
return is_numeric( $number ) ? str_replace( 'x', $this->local_data['thousands_sep'], number_format( $number, $places, $this->local_data['decimal_point'], 'x' ) ) : 0;
}
change to
public function formatNumber( $number, $places=0 )
{
return is_numeric( $number ) ? str_replace( 'x', ',', number_format( $number, $places, $this->local_data['decimal_point'], 'x' ) ) : 0;
}