When sending an PGP/MIME signed (and optionally also encrypted) mail, including signed attachments, KMail puts every attachment twice into the mail.

This double's the size of the mail!

Example mail body, created by KMail. You'll see, that the (very small) file "blue-pixel.png" has become attached twice. But I attached it only once to the mail.
========================================
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="nextPart1782944.DN5yU133gh"; micalg="pgp-sha1"; protocol="application/pgp-signature"
User-Agent: KMail


--nextPart1782944.DN5yU133gh
Content-Type: multipart/mixed; boundary="nextPart4748887.diooyAto5j"
Content-Transfer-Encoding: quoted-printable

This is a multi-part message in MIME format.

=2D-nextPart4748887.diooyAto5j
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"

Small test mail.
=2D-nextPart4748887.diooyAto5j
Content-Disposition: attachment; filename="blue-pixel.png"
Content-Transfer-Encoding: base64
Content-Type: image/png; name="blue-pixel.png"

iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAABmJLR0QA/wD/AP+gvaeTAAAACXBI
WXMAAA3XAAAN1wFCKJt4AAAAB3RJTUUH3gsDDREaJ+YAOQAAAB1pVFh0Q29tbWVudAAAAAAAQ3Jl
YXRlZCB3aXRoIEdJTVBkLmUHAAAADUlEQVQI12NgyDj2HwADyAIu6/Hk0wAAAABJRU5ErkJggg==

=2D-nextPart4748887.diooyAto5j--
This is a multi-part message in MIME format.

--nextPart4748887.diooyAto5j
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"

Small test mail.
--nextPart4748887.diooyAto5j
Content-Disposition: attachment; filename="blue-pixel.png"
Content-Transfer-Encoding: base64
Content-Type: image/png; name="blue-pixel.png"

iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAABmJLR0QA/wD/AP+gvaeTAAAACXBI
WXMAAA3XAAAN1wFCKJt4AAAAB3RJTUUH3gsDDREaJ+YAOQAAAB1pVFh0Q29tbWVudAAAAAAAQ3Jl
YXRlZCB3aXRoIEdJTVBkLmUHAAAADUlEQVQI12NgyDj2HwADyAIu6/Hk0wAAAABJRU5ErkJggg==

--nextPart4748887.diooyAto5j--

--nextPart1782944.DN5yU133gh
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: This is a digitally signed message part.
Content-Transfer-Encoding: 7Bit

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.22 (GNU/Linux)

...%signature data%...
-----END PGP SIGNATURE-----

--nextPart1782944.DN5yU133gh--
========================================

Reproducible: Always