Weird Yahoo Mail Problem

So, my elderly dad has a Yahoo Mail account.

Allofasudden, he starts sending emails to everyone with a large blank
paragraph-sized block above his messages. Many people think he's
sending out blank emails ('cause they didn't scroll down far enough).

I log into his online-only (no pop server involved) account, Compose an
Email and send it, REPLY to an email and send it, FORWARD an email and
send it. No problem. Everything acts as I'd expect....the replied-to
text showing below my reply, the forwarded text showing below my
typed-text, etc.

And I receive all those emails without a blank space showing.

I call my dad (across the country) and tell him to log into his
account, hit COMPOSE MAIL, and start typing me an email. I tell him to
STOP and hit send.

His email comes to me with a large blank space at the top of the
message text! I hit CTRL-A to see if there's anything strange
there....there's not.

But, aha, I hit reply, then again hit CTRL-A and it appears there's an
inserted Table in his message to me. I can't figure out what is
inserting a table by default into an email ONHIS COMPUTER, but not on
mine when I log into his account!

I tried replicating his Inserted Table in IE and in Mozilla.

Any thought out there about how I can resolve this from afar?

Thanks,

Flash
Durham, NC