If I was the user I would expect this two scenarios.
The first is initial settings:
1. insert the mail settings (server, user, password)
2. click Save
3. Wait for the page reload and check the saved configuration
If the user provides a test email address he would also get a test email - even if he did not clicked the 'Send mail' button.

The second one is test of the settings:
1. Insert the email address to test the mail delivery
2. Click 'Send mail'
3. Wait for the email.

It might seem that the 'Send email' button is a bit useless now, because the action is the same as of the Save button. But taken from the point of the user it does what it is expected to do - sends the email with the provided settings. I would see it more as a visual help for the user to identify the option of 'Sending of an email'. Even though the mail settings are rewritten on the backend I don't see that as an issue. 

And there is a second issue, which was the reason why that bug got reopened: If the user would do the init configuration and click on the 'Send email' button, the settings was discarded.