--- a/src-db/database/model/triggers/M_CH_SUBSET_VALUE_TRG.xml	2017-03-01 12:05:25.000000000 +0100
+++ a/src-db/database/model/triggers/M_CH_SUBSET_VALUE_TRG.xml	2017-03-01 12:05:07.000000000 +0100
@@ -60,6 +60,7 @@
       WHERE pch.m_characteristic_id = v_characteristic_id
         AND pch.m_ch_subset_id = new.m_ch_subset_id
         AND exists (select 1 from  m_product where m_product_id=pch.m_product_id AND isgeneric='Y')
+        AND new.m_ch_value_id NOT IN (select m_ch_value_id from m_product_ch_conf WHERE m_product_ch_id=pch.m_product_ch_id)
         AND pch.isvariant='Y'
         AND pch.isexplodeconf = 'Y';
   END IF;