Anomalies with WebHelp Search Results

I have a merged Responsive HTML5 WebHelp project in RoboHelp 11, which I've published to SharePoint. I am seeing some confusing behavior when using the search functionality within the WebHelp. In particular:

With Chrome.......

• If I enter a single word without quotation marks in the search window, I get a page of results. If I open any one of those results, the term that I searched for is highlighted. This is how I would expect the search functionality to work.
• If I enter a two-word phrase within quotation marks, I get a page of results, but the search term is not highlighted when I open one of the results.

With IE11 (which I think is a lost cause for other reasons!)......

• I get the right number of search results, but the search term is not highlighted regardless of whether or not I use quotation marks. This pretty much renders the search functionality useless.

Any advice?