Search Topics includes topics without search term

In testing my .chm output, when I type in a search term and select the 'List Topics' button, the list of topics includes many topics that do not include the search term. I had assumed that the search function was a free text search, and would only include topics where the search term is present. Can someone clarify if my assumption is incorrect, or if there is some configuration change I need to make prior to generating the .chm to ensure only topics where the search term is present are included in the search results?