PayPal HTML buttons broken for large shopping cart

Question

Been battling for weeks with a PayPal Payment Standard FORM problem.

We have been running the same code for many years but noticed our larger invoices (with over 20 items) on them were hitting a white screen of death recently when submitting to PayPal. Testing in the Sandbox worked just fine as before.

After searching everywhere I couldn't find anyone else with this exact problem but noticed if we took the invoice down from say 60 items to 7 items then the invoices seemed to go thru ok. Seems to be a POST buffer problem at PayPals end?

The problem we found was that there is a 502 redirection problem from https://www.paypal.com/cgi-bin/webscr to the new checkout which has /hermes or similar within the URL.

The answer I found was to force the use of the old checkout system at all times using

<input type="hidden" name="force_sa" value="true">

Here is a very simple example with 66 items http://www.whatsanip.com/paypal_bad.html this will hit the WSOD as it is trying to use the new checkout and seems to hit a 502 error when redirecting

BUT

add

<input type="hidden" name="force_sa" value="true">

to the input and we will be sent to the old checkout system which works just great. See same URL as above but swap in _good.html to see the good version that sticks to the old checkout page (i wasnt allowed to add more than 2 links)

Another quirk is that my text editor (Ultraedit) has an in built browser for testing, if submitting from this then it will go thru ok to the old checkout (i think ultraedit is using an old IE implentation).

Any PayPal employees here? Should I submit a bug? If anyone can get _bad.html to work I would be very interested as many hours have been spent investigating this.