In order to test and then execute a campaign I did the following:
- Create simple campaign to send out a single email
- Add a test segment
- Scheduled the send action to a specific date and time (it was yesterday 7pm)
- Wait until the email was sent out to the test segment, review it to make sure everything works fine
- Change the send action to the date when the email should be sent out (it was today at 7am)
- Add the production segment
Result: Every email was sent out three times to contacts in the production segment today at 7am.
PS: The email was marked as transactional email. Maybe marketing email would have helped - still wong behavior of the system, I guess.