You are definitely right. I also have the same thinking.
The guy says that if I wax the car, some portion of the wax will be accidently washed out by either car wash or rain and stay on the windshield. The car wax on windshield causes the problem.

Probably he is right, but I just wax onece and wash twice since I picked up the car. Could it be possible? I doubt.

But anyway the problem is solved CURRENTLY. I will keep watching and post my observation.

Thank you very much for your concern.

try cleaning it with a microfiber cloth...you'll feel it cutting through the crap and then once smooth - it may help prevent it.