I thought you were about to "do a Joanna" and say that you couldn't see some peoples' postings (or vice versa :-)
What I see is that the To: field is blank, but the recipient is underneath with a checkbox allowing his removal. Same applies to Bcc:. So basically, they're editable controls which allow users to be added one at a time, as distinct from many email etc. clients which allow you to (or insist that you) fabricate a comma-separated list with arbitrary quoting rules.
I agree that it's odd, and it has certainly confused me in the past, but it works (for almost everybody, the exception demanding that people use IRC instead).
MarkMLl