The Szenario: You must have 2 Keys, in our scenario it was a S/MIME and OpenPGP Key for the same user.
When right-clicking and select "Sign and Encrypt" option from the menu, either the OpenPGP or S/MIME Key is preselected. When you choose the other Key in the "sign as" field, the "encrpyt to myslef" doesn't get updated to the same key. This sould be changed.