Version:            (using KDE KDE 3.3.1)
Installed from:    SuSE RPMs

It is impossible to attach a message to another message via drag-and-drop and have that attachment signed via PGP/GnuPG.  The resulting message always has a bad signature.  This happens whether the encoding selected is 8-bit, Base64, or quoted-printable.

Steps to reproduce:

0) Set up KMail to work with GnuPG.
1) Message->New Message
2) Fill in header fields as required
3) From the main KMail window, drag a message containing 8-bit characters to the compose window.  It now shows up as an attachment in a subpane.
4) If desired, right-click on the attachment, select Properties, and select either 8-bit, Base64, or Quoted-printable as the encoding.
5) Make sure the message and attachment are to be cryptographically signed (Options->Sign Message) and formatted via OpenPGP/MIME (Options>Cryptographic Message Format->OpenPGP/Mime) using a valid key
6) Message->Send Now
7) View the message you just sent in your sent-mail folder.  Even though you signed it with your own key, KMail claims the signature is bad. (See screenshot attachment.)

There is either some interoperability issues with GnuPG, or KMail is modifying the message after it is signed, or both.

This problem occurs only with drag-and-drop attachments.  If I save an e-mail message to a file and then attach it via Attach->Attach File, then the PGP signature is valid.

I am attaching a sample e-mail message, plus several signed e-mails attaching this message.