This happens on any message where the sender’s name is in RFC 822 format (e.g.: “John Smith” jsmith@acme.com ) . The double-quotes in the name cause the problem.
The temporary workaround is to de-select the option “Include x.509 Certificates when encountered” when using Add Sender to Contacts if the name is an RFC 822 format.
Or, change the email address in the Add Sender dialog to use an RFC 821 format (e.g., jsmith@acme.com ).