Mac Mail Duplicating Entries in "To:"

[RogersDA]

Type in the last name of a recipient, and the suggestions will show. Even though there is only one suggestion based on the name I type, when i click "tab" to accept the name the "To:" will be completed with two entries (same name, same email address).

This happens with many people, but not all. And I've checked - there are no duplicate entries in the Contacts.

Any ideas on how to fix?

EDIT
This only started a few months ago right after I installed Mavericks.

 

[eRondeau]

Weird. Try going into Mail's top menu bar Window -> Previous Recipients and nuke everything in there. Maybe that'll do it.