Why is Mail displaying John Doe?

I upgraded to Yosemite (clean install) last month and didn't notice this over the last few weeks, but one of my Mail accounts is currently showing my name as "John Doe" on all received messages, including those sent years ago, and "John Doe <myaddress>" is shown as the sender :

A similar message from another account is displaying the correct name:

I've disabled all plugins and even restarted the Mac, but the problem persists. Yes, the Full Name on the account is "Don Morris"—any other suggestions?

Ugh. I tried deleting the Mail account and re-adding it—since I'm using iCloud Keychain the account was deleted from my Mavericks Mac and when the account was added back the problem spread to the Mavericks Mac. I deleted it again (from both Macs) and recreated it from Mavericks and the problem persists on both Macs.