This may or may not be related to your issue but I thought I'd throw it out there...
One thing I've noticed in all my cars is that, after a certain period of time, residue builds up on the glass. This residue is invisible and condenses water out of the air much more readily than when the glass is clean. The result is that the glass fogs up unless I constantly have the AC running.
I find myself cleaning the inside of the windshield every couple of months regardless of whether or not it is visibly dirty. I used to use Windex but now worship at the altar of "Invisible Glass". Also, I prefer using a non-terry microfiber towel (
like this one). I find that all of the microfiber terry cloths leave tiny fibers behind that are only visible with the light at a certain angle.