Hi Tom,
Thank you, I did not actually check the front-end, as I did not want to make changes to the search, I only checked the preview, where it worked – sorry about that.
There was another minor problem, where the ‘<' sign in the label was not properly rendered, and was recognized as a HTML tag, causing the disappearance of the settings box. I have corrected that as well. You should see the filter on the front-end now.