Clicking Reset Password produces an error - there is no message in the red panel, but the log shows an InvalidCredentialException - presumably validating a generated password against the regex for the directory.
This error occurred twice in succession (Principal was searched for, details displayed each time) until finally a new password was successfully generated. However, there is only one instance of the exception in catalina.out (was this cached?).

Regex used is:

^(?=.*\d).{8,12}$

There are several items to address here:

1. Display a clean error message when unable to generate a random password.
2. Add instructional text that the random password generator may not be able generated by the internal password generator.
3. Have random password generator make X attempts until a successful password is generator, if not able to display a clean error message.