Hi!
If u have custom fields, and some records is same, it will be show. All the same records.
For solve this problem:
root/components/com_virtuemart/views/category/view.html.php
in ' public function getSearchCustom() ' at line 219
org src: $this->_db->setQuery('SELECT `custom_value` as virtuemart_custom_id,`custom_value` as custom_title FROM `#__virtuemart_product_customfields` WHERE virtuemart_custom_id='.$selected->virtuemart_custom_id);
changed src : $this->_db->setQuery('SELECT `custom_value` as virtuemart_custom_id,`custom_value` as custom_title FROM `#__virtuemart_product_customfields` WHERE virtuemart_custom_id='.$selected->virtuemart_custom_id.' GROUP BY custom_value');
(added "GROUP BY custom_value" statement)