Got it working. My class that was doing my update hadn't referred to
my model file.
The following function might help others... It's preg_matches sha1
passwords and only updates the password field if the password isn't a
sha1 encrypted string.
function after_update() {
$sha1 = (bool) preg_match('/^[0-9a-f]{40}$/i', $this->password);
if (!$sha1) {
$user = R::load('users', $this->id);
$user->password = sha1($this->password);
R::store($user);