[Evolution] Ximian Evolution sends signature as attachment

[kristof <stage01 gawab com>]

If I send a mail with Ximian Evolution 1.4.6 that is encrypted and 
signed the signature is send as an attachment.
This problem arises when I read a mail in Thunderbird that is sent with 
Evolution.

Only if a mail is sent with Ximian Evolution I can see the lock icon of 
the signature.
Signed message from other mail clients show nothing.

Any help would be welcome.