Okay, I figured it was something like that. Thank you for the confirmation.
My philosophy for developing solutions is "if it's there and it can help me finish my task, I should be able to use it." As developers, customers ask us to do all kinds of crazy stuff that sometimes no one has anticipated. As this is a general purpose tool for working with SharePoint lists, I can't help feeling that this web part should give me access to all of the fields in my lists (and libraries).
Please pass on a request to the developers to "track" hidden fields, or at the very least make their tracking a configurable option that can be turned on (either individually or as a group would be fine).
Thanks again for your help.