Version: 1.5.94 (using KDE 3.1.94 (3.2 Beta 2), compiled sources) Compiler: gcc version 3.3.2 (Debian) OS: Linux (i686) release 2.4.22-teb3 Kmail will display inline a attached message which has a "Content-Disposition: attachment" header.
Created attachment 3538 [details] Example output of SpamAssassin which triggers this bug.
I assume you are using the Smart attachment view mode. Marc will tell you why he chose to display attached messages unconditionally inline in smart mode. FWIW, KMail sets the Content-Disposition to "inline" for messages which are forwarded as attachment. IMO the Content-Disposition should always be respected in smart mode.
KMail 1.6.2 (KDE 3.2.2) still does this.
Same behaviour with version 1.10.0 from Kubuntu packages.
I'd say that this is a feature not a bug, and a quite useful one. IMHO, smart mode should assume whatever is easiest to use. If Smart mode just respected whatever is given it was no more smart. However it might be an idea to add an "As given" option that displays inline parts inline and attachment parts as icons.
I would consider this a feature as well. If you don't want attached messages to be displayed inline, you should change to icon view.