The ones I received were proper and well-formed. They had from, reply-to and were legible. I'm using gmail to receive them and had no problems. Some took a couple of days to show up, but the format was correct
I did some more testing, and it now renders correctly in gmail and on the desktop clients I tested with when received via IMAP but not when received via POP. As of last Thursday, it failed with both IMAP and POP. One problem that they did fix between Thursday and Sunday is that they removed a bad character from the "Subject" field.
With IMAP, the server parses the message to determine the content type (such as plain text or HTML) and some key information, while with POP it's all up to the client. When I looked at the raw message, there was clearly still a problem with the header, but obviously the IMAP server and gmail were able to ignore it and handle the message OK, at least now that the bad character was deleted.
So it looks like there is still a problem with how the mail is composed, and it is still non-compliant, but more environments are now able to display it correctly while others still can't.