If the lead is in a flow and they are supposed to receive an email on the next cast, but they have reached their limit, the system will not send them an email. On the next cast after that, the system will try again to send the email, and if their limit has not been reached it will send it.
@Dan - yes what I am stating is the designed behavior. It wouldn't make sense for us to skip the email and never send it if they reached their limits. The system is designed to ALWAYS check, before every cast, to see what has been sent or not.
If you are not seeing this, please call support and log a ticket. I don't see this issue in my testing, but that doesn't rule out a bug.