The confirmation emails appear to be sent as plain text with an HTML copy attached (as is typical for HTML emails); if your email client has been set to display HTML emails you will see that version instead.
The plain text version is Markdown formatted. Yes, that same thing Stack Exchange uses. Markdown is designed to be readable when sent as plain text, and I assume some email clients will render it formatted properly too.
What you are seeing is a Markdown inline link enclosed in a header. It's perfectly valid. What's likely actually happening is your mail client is interpreting the
http://ValidURICharacters as a link, and included the
)### in it. It is both technically valid Markdown and a technically valid URI, so...
An easy fix for you is to use a HTML or Markdown compatible email client (or enable it if you have it disabled). Or you can copy and paste the URL manually; after all, with plain text emails, the clickable link is merely a convenience provided by your email client.
As an aside, Thunderbird appears to highlight the link without the
)### when viewing in plain text mode. I'm pretty sure that's technically incorrect, but it probably works more often.