I am not 100% on this, hopefully someone else will jump in, but I believe something is stripped. (In other word, no there is not a "nut" on the other side you can get ahold of)
The "nut" in this case is made into the windshield frame, it is possible it has broken off and is just turning now. If you didnt before...PB Blaster all them first to give yourself a better chance of them coming out. Let it soak....
Not sure why you are taking this off, but assuming there is some major reason...it is possible you are going to have to drill out the first bolt, etc.
If all this is to simply replace with blinging shiny ones instead, I would say stop now. They have been in there for at least 11+ years at this point and in your case they don't sound like they are coming out ez. Better off to stop/leave the ones in there. (May want to "fix" this one bolt though...)
Sam