Sub categories showing from other Parent Categories

Hi all. When I set up a listing I might choose the parent category “Party Themes” and a sub-category “Halloween”. On a separate lising the Parent category is “Games” with a sub-category “Halloween”. My problem is that when I do a test seach with the only the parent selection “Party Themes” (no sub-category has been selected), I get the games for Halloween showing in the search results. I don’t understand this as this as “Games” is a completeluy separate parent category to “Party Themes” and in any case, there has been no sub-category selected. What do I need to do to ensure I just get what has been selected? All suggestions welcome. Thanks