For a very long time I was using Kmail along with my X.509 certificates to sign emails. This stopped working some time ago (see https://bugs.kde.org/show_bug.cgi?id=417862). Anyone else affected by this issue? It's been months and bug is totally ignored, so either not a lot of people sign their emails with X.509 certificates or I am the only one with this issue and I really would like to discover why.

Note that this only happens with S/MIME certificates. I have no problem at all using gpg keys.

By the way, I have read and followed this instructions in the first place (when it was working):
https://userbase.kde.org/KMail/S_MIME

Any ideas?