UnpackHtml produce empty html-files

When calling the UnpackHtml method on certain emails, we get empty html-files even the method returns one. The GetHtmlBody on these emails works fine. I know the structure is not common, but we get these messages from a Lotus Notes mailer. Is there any workaround without doing this manually ?

Content-Type: multipart/related; boundary="=1="
--=1=
Content-Type: multipart/alternative; boundary="=2="
--=2=
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

--=2=
content-type: multipart/related; boundary=3
--3
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
......