http://www.symantec.com/business/security_response/securityupdates/detail.jsp?fid=security_advisory&pvid=security_advisory&year=2010&suid=20101118_00
If you have a mix of secure and insecure data, and you look at the output, how you you know what parts were "good" and what were not?
For email, we provide annotations that indicate the signed and decrypted parts. We are looking to improve this behavior for current window and other situations where the output has some annotation.