I've noticed that the stop deployment button doesn't seem to work even if clicked well before the deployment has finished. For example, I start a deployment and immediately realize that I've used my default template which does not reboot the target machine after patching, yet I'm pushing a patch that I know will require a reboot. So I click stop while files are being copied. The deployment runs anyway.
I set no-reboot as my default because it's easy to forget to change the default and I don't want to trigger reboots by accident. Configured this way, stop not working is only a minor annoyance.