In the past, I have been able to suspend a send after it started by pressing the suspend button. This time, it is ignoring it. It says it is suspending at the top, but it keeps saying in process and the number of emails send keeps growing. I finally was able to stop it by editing the email, and changing the embargo date to something in the future. I don’t know if this helps, but this send was launched using a cron job.
I should have included that I am using version 3.5.1. I tried it on 3 browsers (firefox on mac and windows, and microsoft on windows).