If a form element is submitted as a GET request, and it contains select elements that have empty or nonexistent name attributes, their remnants still show up in the query string. For instance, if a select element with no name has an option selected with a value of 100, the query string would look like ?=100, when instead that should just be omitted. I included a quick demonstration script as the "URL" of this bug request.
It looks like this is no longer a problem... presumably some other bugfix also fixed this one at some point!
Thank you for checking and following up! I think that I found when it got fixed, marking as duplicate. *** This bug has been marked as a duplicate of bug 20184 ***