As I said in the Post, it is not a security vulnerability itself, but I want to point out that it can be very dangerous to put a password in a GET request.
And the response of ebay is bad too.
But thank you for your constructive comment ;)
EDIT: Sorry for the misunderstanding: as mentioned elsewhere, the problem is not so much the user-agent end, but the hops between where the decryption happens and where the information is used. Why expose the information more than needed there? So I guess ebay's response is a bit lacking. They could make things more secure with relatively little effort.
Except that ebay's response was to the POST over https he mentions in the first section of his article. There is absolutely nothing at all suspicious about that. He wasn't looking into a potential security hole there, he was just prodding as to why they do server-side validation in a completely secure manner. His email had nothing to do with security; he was wasting someone's time asking about implementation details.
He then went on to find a GET version in another area on the site, for which he makes no mention of having sent an email. This might not be considered a security problem to ebay depending how they manage web server logs, but it's certainly a viable inquiry compared to the POST version he did email about.