S/MIME fails with Kleopatra and KMail

Hi,

I'm using kdepim 4.3.3 (and 4.3.2) on Linux and both fail with signing using 
S/MIME. I tried signing eMails using KMail and the Clipboard using Kleopatra 
and both result in a "General Error" without anything useful in the log file 
(even when logging is set to "Guru"). I can safely exclude a configuration 
problem, since signing with gpgsm directly from the commandline works as 
expected (it uses the correct certificate, asks for the passphrase and 
produces a valid signature). Since it fails on two different systems 
(ArchLinux and Fedora 12) I don't expect it to be a local problem.

How can I debug this further? Is this maybe even a "known problem"? Any 
further ideas/advices?

Thanks in advance,
Andreas.