search module problem

Hi,
I bought Ossolution property some days ago and I have a problem with the search module:
I noticed that if I select the main category of my properties, the results don't include the sub-categories. I thought I could solve this problem selecting the main and the sub-category for each property hen I create a new property but it is not allowed.
Is there a way to change it (for example in php files) and have a multiple selection for the category field? Or is there another solution?

thank you

unzip and overwrite these files, it will show sub categories from top level cat in search result... hope it is what you require, Sean