Thanks benn, you just beat me to it. ;-)

After getting some sleep, I started looking at the package source and it became clear that M::L::H contians a M::L and does NOT inherit from it.

However, parse() returns a M::L for the caller to use for sending the email. That's when it HIT ME (doh!). I should have realized what was going on by how the send() was done, ie. via $MIMEmail and not $mailHTML.
So, things are much better now... perhaps it was the sleep? ;-}

Anyhow, that's just another one to add to the lessons learned list.
Plus being new to perl, it's nice get confirmation from someone else, so many thanks for the reply.