interior glass cleaning

If you has used Armorall or other such things on the dash you will never get rid of it. Those type of products off gas and cause smearing of windshields that is something not on the lable. I stopped using Armorall on the interior of all my vehicles years ago and never had the problem again.

Coasty

While I rarely recommend PepBoys they carry a glass cleaner called ClearVue. Best stuff for glass I have ever found. I suspect what you are getting is residue from some conditioner you applied to your dash or seats that is being picked up and circulated by the AC vents. (ArmorAll is one that comes to mind). It tends to keep putting a film on the inside of the glass that is a pain to remove but ClearVue has always taken it right off for me.

I'm a bit late on this thread, perhaps this has been mentioned but the plastic interior gives off a "vinyl vapor" that causes the film on the interior glass even without using a vinyl protectant.