I’m using kmail (not kontact) on KDE4.3 from the Factory repo.
If an email has an attachment, and I want to save it (either click it or right-click > save) kmail pops up two questions (text from memory):
The part <whatever> is encrypted, do you want to keep the encryption?
and
The part <whatever> has a signature, do you want to keep it?
If I click Yes to either of these questions, kmail crashes, if I click No to both, kmail saves a zero byte file.
What’s odd is that the attachment is not encrypted (I sent some to myself from another account). If I choose to open the attachment (eg open a .rar file with Ark) from inside kmail the attachment is opened just fine.
I’ve searched around, but can’t find much to go on.
I have 3 identities, each with 1 account each. The same happens on all accounts/identities.
One of those identities (the default one) had encryption enabled (I have a pgp/gpg key). I have now removed the encryption keys from it (and rebooted as well) but the problem persists. I’d like to use my gpg key as I know a few people who send me signed emails.
Any help would be appreciated cos it is driving me mad 
, but you did the work. I hope it helps, but mostly the reactions on such a bug are coming rather soon.