Hey folks, here's a problem that keeps coming up over and over again, and I'll admit it confused me for some time as well. The refiner web part, for those of you who aren't familiar with it, is used on the search results page in SharePoint 2010. It's designed to give you a faceted search experience, meaning when you execute a query and get search results back, the refiner web part generally shows a few categories of additional metadata elements that apply to all of the search results. When you click on a refiner, it further filters the search results based on the refiner(s) that you have clicked. The values for the refiners themselves come from managed properties that have been crawled. They are a very useful addition to search in SharePoint 2010 and work with both SharePoint Search and FAST Search for SharePoint.
So given their high value proposition, people naturally want to make changes to the web part that renders the refiners. That generally means adding other managed properties to the list of properties that are used in the refiner. I've seen many questions from people though that have made changes to the chunk of Xml that the refiner web part users, they save their changes, execute a query and then don't see their refiner show up. They go back into the web part properties and find that the Xml they modified was in fact not saved. Why does this happen? Well, technically this is not a bug. I'm not saying this is intuitive, but it's not a bug. To change the Xml with the list of properties the web part users, you have to expand the Refinement section of the web part. In that section you will find the Filter Category Definition property, which is where you change the Xml. Now here's the tricky part. Down below that property is a checkbox that says "Use Default Configuration". If you don't uncheck that box, then when you click OK or Apply on the web part, your changes are not saved and your customized Xml is lost. In order to save your changes and use your custom Xml and properties, you MUST UNCHECK this checkbox before saving changes.
This has caused lots of confusion out there, hopefully this post will help you.