Sorry if I'm being dense, but could you be more specific? This feature appears to work as it is supposed to. When I put the cursor in a keyword in the editor and press F1, I get the Help Index dialog with that keyword entered in the the Help Keyword field. This is the same dialog I would get if I select Help > F1 Index Help.
From that dialog, when I click the Help button, I get the correct help topic, which describes how to use and configure this dialog. I don't see anything in the topic about this feature not working.