Chuck - I also noticed on the code that it is different from what Paypal gives as a test php code
They say to use:
$fp = fsockopen ('www.paypal.com', 443,
and classifieds is listed as:
$fp = fsockopen ('www.paypal.com', 80,
It doesn't make a difference in the payment verification - and all the code looks really clean and up to standards. Great job with commenting the code by the way. I'll have to call PayPal and see if it's something that is on their end. Although - it does do what the script intends - returning to the payment_verification.php
It just acts as if there is misbehaving code return in php schema. Almost like a whitespace error of some sort.
I'll keep digging....