Hi Ted! Welcome to our community! 
Special characters like ] are likely best avoided. But given Jay’s reply above I would have thought it would work, just like including % works.
Did you have quotes in your password, perchance? I think " is one that is impossible to use because it encloses the password, unless you edit app.yml to add an escape \.
If that isn’t the answer, then likely yes we need to update this documentation topic to indicate which special characters to avoid! Or update the installer to add a warning?