Fresh image requires reboot before able to login

Hi, I have an instauser script that sets up a local administrator account. To mask the password so my enterprise admin password isn't in a plain script somewhere, I drop the actual password to /private/var/db/shadow/hash, then change the UUID on the hash I dropped to match UUID of the local admin user. This all works, but it requires me to reboot my computer once, sometimes twice before the credentials work. Has anyone else had this problem? Any ideas on how to avoid this? It's not a huge deal, but it might be a time saver if I could avoid this. More details: My instadmg script puts 2 startup scripts in place. 1 is instauser which creates the local admin account. 2 is a post install script. This turns on NTP, sleep settings. ARD, etc. It also sets the hash file with my actual password to match my UUID on my local administrator account. Thanks for any help. -Jeff