Kentico Smart Search not working properly

I created a custom smart index(with analyzer type simple), in the rebuild function I added two lucene documents. One has content "product" and other has content "product" and I have a field "capacity" in both. one's value is 20 and other 40. In my smart search result web part. I choosed my index, search options as FULL, search condition has +Capacity:int(20). I am getting two result after entering search text "Product". I got the search condition as +(Product) +_culture:([en-us TO en-us] [invariantifieldivaluei TO invariantifieldivaluei])+capacity:10000000020 by debugging smart result web part. I pasted that condition in Luke tool. Its showing 1 result.I am expecting kentico result to be 1 but its 2. Is this a bug in kentico? I am using Kentico V12