I am using Webmin 1.620 on Ubuntu 11.04
I created a new upstart service and was surprised that in would not run on a reboot after power loss, but it did run after a normal reboot
Googling I found that for Ubuntu level 11 on it seems you need to run a program called
update-rc.d <filename> defaults
in order to make the service work on all boots.
Maybe you can add this for Ubuntu users?