I have had the exact same problem. It happens with me using Outlook on my desktop. It has happened with three people I have sent emails to in the past year. I will type in the email address I want to send it to. Not auto loaded, but actually typing the full email. That email address shows up in the To: box just fine. I hit send and it sends it to another email address for that person. I see this because I go to my sent folder and I see it was sent to their other email address and not the one I typed.
This is extremely frustrating. I have had to go in and delete all their email addresses from their contact information and retype the email addresses. That sometimes fixes the problem but then the problem will occur again with another person. This is a major problem that Microsoft needs to resolve.
