My SEAT does this.
Thought it was just dirty windows (all of them inside) so cleaned them and they were that grimey i had to use soapy water to de-grease them.
The moment i put the blowers on, the aircon or it rains it just fogs up inside and the greasy filmy type layer on the windows returns, it does clear itself, but when you touch the windows again or put them up and down, it leaves smear marks !