Hi,
I experienced the same problem last weekend. Wanted to pay via PayPal from the
CP site, was forwarded to PayPal, saw the correct amount there, pushed "OK",
was forwarded back to CP. Cart not paid.
Tried the same with credit card, it worked. I immediately changed my PW on PayPal,
I hope it was just a bug, not a DNS attack.

Best regards,
    Michael