One more followup on this – here’s what I found – after I paste the form code in to the editor in HTML mode, if I then edit the form in Visual Mode (say add heading formatting) then it changes the form code. I just re-did the form with new code from PayPal and I double checked their code and it was correct. After I switched to Visual Mode the selector box once was not working right. When I went back to HTML to check it had added the unneeded <Select> formatting.
So basically once you add the code in HTML you cannot then edit anything about the form in Visual Mode or it makes changes.