Moving this from a downstream bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=607392

Evolution creates a copy of a message, when the user changes the email account
that he/she wishes to use to send the email, instead of changing just the used
account.

Version-Release number of selected component (if applicable): 2.30.1.2

Steps to Reproduce:
1. Create a new email, using your default email account (you must have more
than one account to experience this bug)
2. Press the "Send" button.
3. Open the "Outbox" folder and open the message, before it being sent.
4. Change the account you wish to use to send that email (example, change from
the default one, to a secondary one).
5. Click on "Send".
6. A copy of the message is created, instead of replacement the original
message

Actual results:

Two emails, from two different accounts, that are exactly the same are sent.

Additional info:

This bug started in Fedora 13. Didn't exist on Fedora 12.