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.
It was tested with gpg4win 3.0.1 on Windows 10 64bit with Outlook 2010 64bit.