Jeff Roberts updated September 6 at 9:22 AM
Due to the auto-save feature of some mail clients such as in Mail.app, you may see duplicate draft messages when using the IMAP protocol.
To fix this, go to the following menu from Mail.app:
Mail > Preferences > Accounts
Select the IMAP account on the left and click the Mailbox Behaviors tab.
From the Draft Mailbox: pull down menu change your Drafts from [Gmail/Drafts] to the Drafts folder on your local machine.
This will cause your Mail app to stop syncing drafts with the email server.
The downside to this fix is that drafts written on your devices will not sync to the server and therefore your other devices.