Tahoe Forces an E-mail Address from Contacts

This is weird - just started happening today:

When I start typing in an E-mail recipient's address (Name@Domain.com), Mail tries to autofill (as normal). However, when I get to a unique part of the address, Mail is still forcing an incorrect address from my Contacts!

Wait, what?

Example: I want to send to "MattG@exdomain.com" which is not in Contacts. In Contacts is "MattDog@otherdomain.com"

Normally, as I begin typing, the Autofill comes up with a list of "Matt" options until I get to "MattG..." - which is where it becomes unique. At that point, Autofill goes blank and allows me to finish → "...@exdomain.com".

Starting today (that I can remember), no matter how much of the "new/unique" address I type into the field (including the entire, "MattG@exdomain.com"), Autofill stays active and Mail is forcing the entry of "MattDog@otherdomain.com" - from my Contacts.

What is going on here?

Matt