I've been using WFP 7 years... I get the occasional problem window...
I cleaned a new customer last week... A new build house, lots of dust on the windows and in the window vents, the sun was very hot directly on the 4 top back windows, they were drying too quickly and leaving dirty streaks all down the glass from the vents... I tried cleaning them 4 times WFP, but same results each time - I got the ladders off the van and trad'ed them! I'll see what happens on the next clean.
Andy